S98 



MUSEUM OF ANIMATED NATURE. 



[CnVSTACEA 



cone, and of which a triple i»*ries is seen ; c is the 

 younjC iihell of the natural size adhering to a portion 

 of rock ; d is the same magnified, and placed in such 

 a position as to show the operculum, and the pointed 

 ends of the additional pieces with which the shelly 

 cone is firat strengthened, before an additional layer 

 is added or the points have become eroded. 



Another and very curious genus established by 

 Mr. Sowerby is Octomcris. The cone consists of 

 eight pieces, their sutures internally exhibiting an 

 angular configuration ; the shelly pieces are exter- 

 nally foliaceous ; there is no internal plate; a thin 

 epidermis is observable ; the operculum consists of 

 four parts. As an example, we give Octomeris an- 

 gulosa, Sowerby, Fig. 3093 : a represents the shell 

 in such a position as to show the operculum and the 

 eight foliated pieces of the cone ; c, d, e,f, g, h, i, k, 

 represent the eight pieces separated and present- 

 ing their internal surface : c, the anterior piece ; 

 d, the posterior piece ; /, the operculum, consisting 

 of four pieces, of which the two anterior are the 

 lareest. 



With respect to fossil specimens of the shells of 

 the Cirrhopoda, they appear to be of rare occur- 

 'vnce ; fragments of Pentalasmis from the Calcaire 



grossier of Grignon, and the Suffolk crag, have been 

 met with, and fossil balani have been found in tertiary 

 deposits, and species are recorded from the beds of 

 Piacenza, Bordeaux, Paris, Essex, &c. Here, then, 

 we terminate our sketch of the Cirrhopoda, which, , 

 enclosed as they are in shelly cases, few, we think, i 

 will consider as immediately allied to the bivalve 

 teslacea. Their symmetrical limbs and nervous sys- 

 tem are distinguishing characteristics of great im- 

 portance ; and with respect to the shell and mantle, j 

 which, if analogous to the same parts that envelope [ 

 the mollusks, would certainly determine an approxi- | 

 mation between the two groups: even these parts, , 

 according to Professor Burmeister, are essentially j 

 different, and bear more resemblance to the external 

 covering of the Crustacea than that of the mollusca. 

 We may here also revert again to the singular 

 transformations which the young of the Cirrhopodi 

 undergo after exclusion from the egg, and of which, 

 if the observations of Cavolini, of Mr. Thompson, 

 and Professor Burmeister be verified, some of the 

 Crustacea, as the common crab, also afford exam- 

 ples. The changes of the young cirrhopods from a 

 state of freedom, and from a comparatively perfect 

 organization, with eyes and limbs adapted for swim- 



ming, to a fixed condition, and to a modification of 

 structure destitute of organs of sight and locomotion, 

 is indeed very surprising. Startling as the fact 

 may be, there is no reason to doubt the correctness 

 of Mr. Thompson's statements. It must then be 

 concluded that on entering into life the little crea- 

 tures are free agents, and possessed both of that 

 peculiar instinctive impulse which urges them to 

 seek a place of permanent rest, and of that instinc- 

 tive knowledge which enables them to determine 

 upon that suited to their specific habits. Hence 

 then does each species select its proper abode, the 

 coral mass, the sponge, the log of wood, the rock or 

 stone, or the skin of the whale, the shell of the tor- 

 toise, or the valves of mollusks reposing at the bot- 

 tom of the sea. Having once fixed upon their 

 resting-place, and there settled, the transformation 

 begins, and the once active cirrhopod is moored or 

 fastened closely throughout its future term of ex- 

 istence ; to this new mode of life is its novel organi- 

 zation adapted; its cirrhi enable it to prey on the 

 minute tenants of the water; its shell defends it; it 

 grows rapidly, and fulfils the part allotted to it in 

 the grand scheme of creation. 



ARTICULATA, Cuv. (HOMOG^S^NGLIATA, Owen.) 



Tm term Homogangliata, proposed by Professor 

 Owen as the designation of this great group or sub- 

 kingdom, alludes to the condition of the nervous 

 system,— the term Articulata to external conforma- 

 tion, the body being composed of a series of rings 

 formed by the skin or integument, which may be 

 soft as in the worm and leech, or hard and serving 

 as an external skeleton, as in the beetle, the crab, 

 and the lobster. 



With respect to the nervous system, it consists of 

 a series of ganglions symmetrically disposed along 

 the ventral region of the body united by intervening 

 nervous filaments so as to form a continuous chain. 

 The first, or anterior pair of ganglia are an excep- 

 tion, as far as position is concerned, to the rest, 

 being placed on the dorsal aspect of the body ; they 

 give off a nervous ring which embraces the oeso- 

 phagus, and communicates with the succeeding 

 ganglia. These oesophageal ganglia also give off 

 nervous filaments to the head, the organs of vision, 

 hearing, taste, &c., and being in some degree devoted 

 to the perceptive faculties, have been regarded as 

 analogous to the brain in the higher orders. The 

 other ganglia in succession give nerves to the re- 

 spective segments of the body to which they belong. 

 In the higher Crustacea the oesophageal ganglia are 

 consolidated into one, and in numerous instances 

 certain of the succeeding ganglia become blended 

 into single ones, so as to form a few concentrated 

 nervous centres. 



As may be inferred from the arrangement of the 

 nervous system, the body in the Homogangliata is 

 symmetrical. Where limbs exist we find them dis- 

 posed in equal order and number on each side ; and 

 there are distinct sanguiferous and respiratory sys- 

 tems. Among the Homogangliata, the various groups 

 or classes differ much from each other in form and 

 characters; in habits and modes of life. Some are 

 aquatic, some terrestrial; and every mode of pro- 

 gression from crawling to swimming and flying is 

 exhibited among them. 



We have said tha't the framework of the Homo- 

 gangliata, or Articulata, consists of a series of rings 

 of greater or less density either composing the in- 

 teguments themselves or else added to them, and 

 constituting a kind of external skeleton, both for 

 the attachment of muscles and the protection of the 

 internal parts. 



In the lowest groups the rings are soft and nume- 

 rous, and the body is elongated ; these beings, such 

 as the leech, worm, &c., have no true limbs, though 

 appendages of use in progression are allotted to the 

 various segments. In the higher groups the limbs 

 are well developed, and in one class we find wings. 



CLASS CRUSTACEA 



. (Chabs, Lobstkrs, &c.). The Crustacea are all, or 

 almost all, aquatic in their habits, and have their 

 organs of respiration modified for the element they 

 naturally tenant. In their bodily conformation they 



. do not depart from the annulose model, though the 

 rings in the higher groups of the class coalesce to a 

 greater or less extent, accompanied by an according 

 concentration of the nervous system. In the lower 

 groups, indeed, the annulose conformation is main- 

 .tained, as in the Myriapods (Centipedes, &c.), and 



each segment has its limb subservient to locomotion. 

 If with Latreille, Lamarck, and others, we place the 

 Woodlice (Oniscus, Porcellio, and Armadillo) within 

 the pale of the Crustacea, we have in them a link 

 immedia>-'ly in connection with the Myriapods, 

 whence through the Ligia oceanica, or marine onis- 

 cus, and other allied genera, we advance to the 

 genus Cyamus (subgenus Leptomera), and then pass 

 on to theSandhoppers, as Talifrus, Gammarus, &c., 

 and then to Squilla, Lucifer, &c., and so on to the 

 Shrimps (Crangon), the Prawns (Paaelmon), the 

 Lobsters, and the Crabs. 



It is in these last that the greatest centralization 

 of the system presents itself, the rings being sol- 

 dered into a single carapace covering the anterior 

 part of the body, and the nervous ganglia equally 

 coalescing. 



The Crustacea are invested either with a horny 

 tegumentary covering, as in the shrimp, or with a 

 mail of considerable hardness, composed of car- 

 bonate of lime, as in the lobster and crab. This ar- 

 mour is, indeed, an external articulated skeleton, 

 secreted by a vascular dermis or skin, and is at in- 

 tervals thrown off and renewed. 



We may here observe that in Latreille's arrange- 

 ment the Crustacea primarily resol ve themselves into 

 two great sections, the Malacostiaca* (soft-shelled 

 animals) and Entomostraca (shelled insects). It is 

 to the fii-st section that we shall at present confine 

 our attention. 



The modes in which the Crustacea have been 

 classified are almost as various as the writers who 

 have made this department of zoology their study. 

 That of Milne Edwards is that to which preference 

 is to be given. It does not differ in material points 

 from the simplified table subjoined. 



Malacostraca. 



Orde) 



Eyes on peduncles, and moveable. 



iBrachyura — as Crabs. 

 Anomurat — as Hermit Crabs, Birgus, &c. 

 Macrura — as Lobsters. 

 „, , jUnipeltata — as Squilla. 



^'"•"^P"''* \Bipeltata-.as Phyllosoma, Lucifer, &c. 



Eyes sessile and immoveable. 



Amphipoda — as Gammarus, Talitrus, &c. 

 Lsemodipoda — as Cyamus, Leptomera, &c. 

 Isopoda — as Ligia, Limnoria, Canolira, Oniscus, Ar- 

 madillo. 



Id order to understand the general structure as it 

 obtains in the higher Malacostraca, let us take a 

 familiar species, the Common Lobster, and atten- 

 tively examine its organization. In the first place, 

 then, we observe that the head and thorax are, as it 

 were, blended into one piece, and covered by a 

 dorsal shield or carapace, furrowed where the di- 

 vision between the head and thorax extends. To this 

 portion, called Cephalothorax, succeeds an abdo- 

 minal portion covered with seven rings of armour, 

 broad above, capable of motion, hinged upon each 



• Malacostracfi, from fioAaxoc, soft, ofrrpaitov, a slioll. The name, 

 alluding to the softnew of the shell compared with that of a bivalve 

 or univalve mollusk, is not, it must be confessed, very happily 

 chosen. It is, however, very generally adopted. 



f MacrurA and Anomura are generally spelled Macroura and 

 Anomoura, and if so, Uracliynra ought to be Brachyoura. 



other, and regularly overlapping each other's edges 

 in succession. Of these the last may be regarded 

 as the caudal or tail-ring ; it has two oar-like plates 

 on each side, of which the outermost is transversely 

 jointed. We may here observe that Audouin and 

 Milne Edwards consider the Cephalothorax to con- 

 sist essentially of fourteen rings, viz., seven for the 

 head, and seven for the thorax, so that with those of 

 the abdomen there are twenty-one altogether. 



The limbs are divided into three sets; on each 

 side of the mouth are six limbs, termed jaw-feet 

 (pieds-mSchoires), which are furnished with tentacu- 

 lar appendages. These limbs manipulate the food, 

 turn it about, and apply it to the powerful jaws. 

 Under the chest are based five pairs of true limbs. 

 Of these the first pair are remarkably developed, 

 possessing vast power, and the last joint presents us 

 with pincers or chelae, acted upon by voluminous 

 muscles. In some Crustacea the chelae are the same, 

 but in the lobster they differ : the left pincer has 

 its opposing edges finely dentated, and is used for 

 seizing, cutting, or rending prey. The right is 

 bluntly tuberculated, and is adapted for holding 

 anchor-like upon any fixed object in order to moor 

 its possessor amidst the agitated waters. Of the 

 four succeeding limbs on each side the two first end 

 in small pincers, the rest in pointed articulators. 

 Along the under surface of the abdomen (often 

 called the tail, but erroneously) are certain articu- 

 lated appendages, termed false feet : there are five 

 pairs, and all, excepting the first pair, which are 

 simple, are bifid at the last joint. These false feet 

 are not used in locomotion, but are of service in the 

 case of the female in enabling her to affix the roe 

 or eggs to the under surface of the abdomen. An- 

 teriorly the carapace projects in the form of a den- 

 tated spine, protecting the eyes, two in number, 

 placed on short moveable footstalks or peduncles. 

 Below the eyes are four antennae, of which the 

 central pair are the shortest and slenderest, and 

 they are also bifid. 



In ascending the scale of beings from the lowest 

 grades of life to the highest, the Crustacea are the 

 first in the scale to present us with definite organs 

 of hearing ; for though insects hear, the organs 

 themselves have not been detected, though, most 



firobably, they reside at the base of the antennse. 

 n the lobster they are placed on the basal joint of 

 the larger pair of antennae underneath, and appear 

 in the form of a minute tympanic membrane, sur- 

 rounded by a slightly elevated margin. This mem- 

 brane covers a little cell filled with fluid, and a 

 minute branch of the nerve supplying the antenna; 

 ramifies upon it. 



The mouth of the lobster is vei-y complicated ; it 

 is furnished with two mandibles, two powerful max- 

 illae, and two maxillary palpi. The shell forms a 

 labium, or sort of upper lip, but there is no distinct 

 labium, or lower lip. 



In the Macrura, of which the lobster is an ex- 

 ample, the abdominal portion is the great organ of 

 locomotion ; hence the muscular development which 

 it displays. It is by striking the water with a vigor- 

 ous flap that the lobster propels itself aiong ; and 

 the caudal paddles are so arranged that when the 

 tail is extended they slide over each other so as to 

 present the least possible surface to the water, but 

 during the stroke they expand. In accordance with 



