326 



MUSEUM OF ANIMATED NATURE. 



[ISOPODS. 



fied. The rollowin? genera form a family ifroup 

 called Idoteidx. Tlie branchiaB are in llie form of 

 bladdera capable of bein); inflated, and covered by 

 two blades or valvules of the last segment, to the 

 aides of which they are affixed. The tail is formed 

 of three segments, the last of which is the largest, 

 without appendages at the end or lateial fins. All 

 are marine. In the genus Idotea the feet are 

 strongly ungniciilale. Fig. 3J3U represenu the 

 Idotea tricukpidata. 



The genus Slenrtsoma differs principally in the 

 (Treat length of the lateral antennae. The Stenosoma 

 lineare (Kig. 321)0) is an example, a, laminae of 

 the under part of the abdomen. 



Passing over one or two genera we come to 

 Asellus, the representative of a distinct family group, 

 Asellota. In the genus Ai-ellus there uie two bilid 

 slender filaments at the caudal exlreniiiy of the 

 bo<ly. The two central antenna; are long, the two 

 others as long as the peduncles of the former. The 

 feet are unguiculate, and fringed. The Asellus 

 aquaticus is represented at Fig. 3201. The speci- 

 mens are those of a female magnitied ; the line be- 

 tween is the natural length, a, upperside ; b, under- 

 side. 



This singular Isopod is a native of fresh water, 

 and is abundant in stagnant pools, or slow-moving 

 drainage courses ; we have found it in plenty in slug- 

 gish drains, buried in the mud, or among decompos- 

 ing masses of leaves and herbage. It is by no means 

 rapid in its aquatic movements, but when disturbed 

 buries itself very promptly ; it remains in a state of 

 torpor during the winter, thus protected in its retreat 

 from the severities of the season. In the spring it 

 emerges, and returns to active existence. The male 

 exceeds the female in size. The eggs of the latter 

 are contained in a membranous sac placed between 

 the limbs under the chest, and this sac opens by a 

 longitudinal slit to give passage to the young. It 

 appears to feed on decomposing animal and vege- 

 table matters. 



We now come to another family group termed 

 Oniscidie, of which the ordinary woodlouse is the 

 type. 



In this family the antennae are indeed four, but 

 the two intermediate ones are extremely minute. 

 The tail is composed of six segments, with either 

 two or four needle-shaped appendages at the poste- 

 rior border of the last segment, which has no lateral 

 fins. Some species are aquatic, others terrestrial ; 

 and in the latter the first leaflets below the tail 

 exhibit a row of small holes where the air pene- 

 trates to the organs of respiiation there inclosed. 



In genus Ligia, the stem of the lateral antenniE is 

 composed of a great number of small joints, and the 

 caudal stylets are bifid. 



The Ligia oceanica (Fig. 3262) is common on the 

 sea-coast, and may be seen creeping about on rocks 

 or the parapets of marine structures ; when disturbed 

 it folds up its limbs and lets itself drop. It closely 

 resembles the woodlouse in appearance, but is larger, 

 being an inch in length ; its colour is grey with two 

 large yellow marks on the back, a shows the upper 

 surface ; b, the under surface, natural size. The 

 Ligia Italica, and Ligia Hypnorum, are allied spe- 

 cies. 



We now come to the genus Oniscus, of which the 

 ordinary Woodlouse, or Cloporte of the French, is an 

 example. 



In this genus the lateral antennae have eight 

 joints, and the two external appendages of the tail 

 are longer than the two intermediate. 



Fig. 32t)3 is the common Woodlouse, Oniscus 

 murarius. This species is abundant in damp or 

 humid places, secreting itself during the day under 

 stones beneath the baik of mouldering logs or 

 trees, in the holes of walls, in the ground at the base 

 of garden pales, in cellars, &c. They creep abroad 

 during the hours of daikness, in search of decom- 

 posed animal and vegetable matters, on which they 

 feed; and retire on the approach of dawn. Their 

 movements are by no means rapid, and when 

 alarmed and unable to escape they double them- 

 selves up, but do not form a complete ball. The 

 eggs are inclosed in a pouch beneath the chest. 

 The young when exchuled have a thoracic segment 

 short, and consequently only six pairs of limbs, in- 

 stead of seven. These animals were formerly used 

 in medicine, but have been long rejected from the 

 materia medica. Latreille separates from the genus 

 Oniscus such woodlice as have only seven joints in 

 the lateral antennae ; of these he forms the genus 

 Porcellio. We may notice as examples the Clo- 

 porte ordinaire, var. c. Geoffroy, Oniscus asellus of 

 aulhoi-s ; and the Cloporte ordinaire, var. b. Geoffroy, 

 Porcellio Isevis, Latr. 



In the allied genus Armadillo, the animals have 

 the power of rolling themselves up into a complete 

 little ball; the posterior appendages of the body are 

 not projecting, and the last segment is triangular. 

 The lateral antennm have only seven joints ; the 

 upper subcaudal scales are pierced with a row of 

 •mall orifices. 



The common Armadillo, A. pustulosus(Fig. 3264), 

 is well known, inhabiting the same situations as the 

 woodlouse, and remarkable for its habit of rolling 

 itself up into a little motionless ball when touched. 

 It is the Oniscus Armadillo of Linnaeus, the Oniscus 

 cinereus of Panzer, the Armadille pustulf of Des- 

 marest; but not the Oniscus piistulatus of Fabricius 

 and Panzer, which is the Glomaris marginata of 

 I^ach, and the lulus ovalis of Linnaeus, one of the 

 Millepedes. (Myriapoda.) 



Retelling to Fig. 3264, a shows the Armadillo 

 pustulatus expanded ; b, rolled up. 



Here, then, with these well-known terrestrial 

 creatures so familiar to all, we may close our sketch 

 of the Isopoda ; but perhaps we cannot select a more 

 appropriate place for arranging our pictorial speci- 

 mens of the Trilobites, singular forms known only 

 in their fossil state, and to which we have already 

 alluded. 



M. Latreille considers the Trilobites as related to 

 the King-Crabs (Xiphosurus), and Mr. MacLeay 

 regards them as constituting a distinct order inter- 

 mediate between the Isopods and some of the En- 

 tomostraca, as fur example Apus. " If," says Mr. Mac- 

 Leay, " the Trilobites are once demonstrated to have 

 possessed articulated feet, it will be difficult to re- 

 move a male Bopyrusfrom the group. Here the two 

 eyes jre placed on the back of the head, and wide 

 apart. Here also there are no antennae, no poste- 

 rior lateral abdominal appendages, and besides no 

 very distinct articulation to the sternum. If the 

 Bumastus (a trilobite) of Murchison had a body of 

 thirteen equal segments, with short crustaceous feet, 

 it would be a male Bopyrus, so close is the affinity. 

 (See Fig. 3i48 ) The differences between a male 

 and female Bopyrus, such for instance as the pre- 

 sence of eyes in the former, and the want of them 

 in the latter, may also induce us to fancy that similar 

 resemblances may possibly have occurred between 

 certain male and female Tiilobita, which from their 

 primii facie difference of form are now placed in 

 distinct genera, though they may have truly be- 

 longed to one and the same species." 



The Trilobites (called Dudley Fossils, Entomoli- 

 thus paradoxus, &c.) are found in certain strata, 

 throughout every part of the globe. They occur, 

 says Dr. Buckland, all over Northern Europe and 

 in numerous localities in North America; in the 

 southern hemisphere, they occur in the Andes and 

 at the Cape of Good Hope. " None have been found 

 in any strata more recent than the carboniferous 

 series, and no other crustaceans, except three (orms 

 which are Entomostracous, have been noticed in 

 strata coeval with any of those that contain the re- 

 mains of Trilobites ; so that during the long periods 

 that intervened between the deposition ol the earliest 

 fossililcious strata, and the termination of the coal 

 formation, the Trilobites appear to have been the 

 chief representatives of a class which was largely 

 multiplied into other orders and families, alter 

 these earliest forms of marine crustaceans became 

 extinct." 



In our country the transition limestone of Dudley 

 affords many interesting species of Trilobite, and 

 the form occurs in the black marble at Ashford in 

 Derbyshire, but is very rare. 



As already observed, whether the trilobites pos- 

 sessed antennae and limbs is yet undecided ; they 

 were, however, provided with highly organized in- 

 struments of vision, — simple as it would appeal- in 

 Bumastus, but compound in the rest. 



Dr. Huckland remarks that the eyes of Trilo- 

 bites deserve peculiar consideration, as affording 

 the most ancient and almost the only example 

 yet found in the Ibssil world of the preservation of 

 parts so delicate as the visual organs of animals 

 that ceased to live many thousands and perhaps 

 millions of years ago ; indeed we must regard those 

 organs with feelings of no ordinaiy kind, when we 

 recollect that we have before us the identical in- 

 struments of vision through which the light of 

 heaven was admitted to the sensorium of some of 

 the fii-st-created inhabitants of our planet. 



According to Dr. Buckland each eye of Asaphus 

 caudatus contains at least four hundred nearly sphe- 

 rical lenses fixed in separate compartments on the 

 surface of the cornea, and he observes that the form 

 of the general cornea is peculiarly adapted to the 

 uses of an animal destined to live at the bottom of 

 the water : •' to look downwards was as tnuch im- 

 possible as it was unnecessary to a creature living 

 at the bottom ; but for horizontal vision in eveiy 

 direction the contrivance is complete. The form of 

 each eye is nearly that of the frustiumof a cone, in- 

 complete on that side only which is directly opposite 

 to the corresponding side of the other eye, and in 

 which, if facets were present, their chief range 

 would be towards each other across the head, where 

 no vision was required. The exterior of each eye, 

 like a circular bastion, ranges nearly round three- 

 fourths of a circle, each commanding so much of 

 the horizon, that where the distinct vision of one 

 eye ceases that of the other eye begins ; so that in 



the horizontal direction the combined range of both 

 eyes was panoramic." Dr. Buckland then icfei-s to 

 the modifications of the same mechanism in the 

 existing Brancliipus, Sciolis, and Liniulus, accord- 

 ing to their habits, and remarks that we find in 

 Trilobites of the transition rocks, which were among 

 the most ancient forms of animal life, the same 

 conformation of the eye which is at present adapted 

 to similar functions in the living Scrolls. 



Fig. 3-J65 represents the Asaphus caudatus, from 

 Dudley, with the eyes, n, a, well preserved. 



Fig. 326G shows at a, a side view of the left eye 

 of the same highly magnified ; b, a magnified por- 

 tion of the eye of Calymene macrophthalmus. 

 Most, if not all the Trilobites, had the power of 

 rolling themselves up somewhat in the manner of 

 a woodlouse ; in this position the head was not con- 

 cealed, but, toad-like, surmounted the ball or hinder 

 segments, curled round, producing a grotesque 

 effect. Of what extent of locomotion they were 

 capable, we are unable to say with certainty. 



Referring to our pictorial specimens, Hg. 3267 

 represents the under surface of the anterior por- 

 tion of the shield of Asaphus platycephalus, from 

 Lake Huron. 



Fig, 3268 is the Nileus Armadillo : a, seen from 

 above ; b, profile, the animal rolled up. 



Fig. 3269, Calymene Browningii, partially rolled 

 up. 



Fig. 3270, Paradoxo'ides Tessmi. 



Fig. 3271, Trinucleus Lloydii. 



Fig. 3'272, Agnostus pisifoirais, one of the anoma- 

 lous Trilobites of Battoids, which differ in many 

 points from the true Trilobites, and are as yet but 

 very imperfectly known. The fossils resemble small 

 and nearly circular bucklers of two kinds; and M. 

 Brogniart considers them to have covered the whole 

 of the body, but M. Dalman to have belonged some 

 to the head, others to the abdomen of a Trilobite, 

 the thorax of which was rudimentary. 



Figs. 3273, 3274, two species of Trilobite. 



SECTION ENTOMOSTRACA. 



The Entomostracous Crustaceans are all aquatic, 

 and for the most part inhabitants of fresh water; 

 many are microscopic. They chiefly abound in 

 stagnant pools or sluggish streams, yet the purer 

 rivers and fountains are not without their species. 

 Microscopic plants and animalcules are their food, 

 including the dead of their own race ; and they in 

 turn are the prey of the Hydra, and of aquatic 

 larvae. Many, as the Cyclops, common in every 

 ditch, undergo singular translormations in their pro- 

 gress from the egg to maturity. 



The females of many species carry the eggs in 

 a sac or in sac-like appendages, and in Apus the 

 eleventh pair of legs have their first joints ex- 

 panded into two discs, which closing together I'orm 

 a sort of bivalve chamber in which the eggs are 

 contained. 



Latreille divides the Entomostraca into the fol- 

 lowing ordei-s and tribes : 



Order Branchiopoda. Sections j Lophyropa. 

 or Tribes ( Pliyllopa. 



Order Piecilopoda \ J.yphosuia. 



'^ t aiphonostoma. 



The Lophyro])a are divided into— 1st, Carcinoida, 

 with one eye, as Cyclops ; with two eyes, as Zoea : 

 2nd, Ostracoda or Ostrapoda, with one eye, as 

 Cypiia : 3id, Cladocera, as Daphnia. 



The Pliyllopa are divided into — 1st, Ceratophina, 

 as Bianclupus ; 2nd, .^spidophoia, as Apus. 



The Xyphosura are not divided ; as we shall see, 

 they constitute an order or sub-class per se. 



The Siphonostoma are divided into — Ist, Cali- 

 gians, as .'\rgulus, Caligus, &c. : and 2iul, Lernaei- 

 formians. as Nicothoe, &c. The arrangement of 

 Milne 1-dvvards differs considerably and may be 

 summed up as follows. 



Bb.ancihopoda. — No true branchiir, but the 

 thoracic extremities lamellar, membranous, and 

 lespiralive. Orders: — 1. Phyllopoda : no bivalve 

 shell-like covering, limbs natatory, from eight to 

 eighty-two. (Ex. Brancliipus. Pliyllopus, Apus.) 

 2. Cladocera: carapace like a bivalve shell, thoiacio 

 limbs five pairs. (Ex. Daphnia, &c.)' 



Entomostrac.i (proi)er). — No branchiae nor any 

 apparent respiratory organs ; eyes sessile, united 

 into a single mass. Orders: — 1. Copepoda : body 

 divided into distinct rings, neither carapace, nor 

 valvular shell ; thoracic and oral members nu- 

 merous. (Ex. Cyclops.) 2. Ostrapoda: body with- 

 out evident annular divisions, inclosed in a bivalve 

 shell ; limbs few. (Ex. Cypris, Cytherea, &c.) 



Hausteli.ata (Suctorial crustaceans).— Orders : 

 — 1. Araiiaeilormes : extremities rod-like, long, and 

 adapted forwalking. (Ex. Pychnogonum, Nymphon.) 

 2. Siphonostomata : extremities not adapted for 

 walking ; partly lamellar, partly prehensile. (Ex. 

 Dichlcstion, Argulus, Nicothoe, &c.) 3. Lernaei- 

 fornies : extremities rudimentary ; body presenting 

 abnormal lorms. (Ex. Lerna-a, &c.') 



