90S 



STOMAPODA. 



STOMAPODA. 



936 



of five laminae, or blades, disposed in a fan-shape,, as in the Macrourous 

 Decapods. The carapace descends on each side against the base of 

 the feet ; covers the whole, or nearly the whole, of the thorax, as well 

 as the head ; and presents only a rudimentary rostrum in front ; 

 there is no moveable plate in place of this frontal prolongation, as in 

 Squilla, and the ophthalmic ring is in general very short and naked. 

 The disposition of the eyes, of the antennae, and of the pieces of the 

 mouth, varies. The thoracic plates are all slender, natatory, and 

 resemble each other ; but their number varies much. The abdomen 

 is composed, aa ordinarily, of seven rings, the first five of which 

 carry natatory false feet ; whilst the seventh forms, with the append- 

 ages of the sixth segment, the caudal fin : these last appendages 

 consist each of a small very short basilary joint, and of two great 

 terminal plates disposed as in the Macrourous Decapods. Finally, the 

 conformation of the respiratory apparatus varies; sometimes the 

 branchiae do not exist ; sometimes vestiges of them are found at the 

 abdominal false feet ; and sometimes they are, on the contrary, very 

 much developed, and suspended under the thorax. (Milne-Edwards.) 



M. Milne-Edwards divides the Caridoids into two small tribes, the 

 Mysians and the Luciferians. 



1st Tribe. Mysians. 



This tribe resembles the Salicoques so closely, that till lately the 

 species forming it had been arranged under the Macrourous Decapods, 

 where they constituted the family designated Schizopods. 



The carapace extends to the base of the ocular peduncle?, and 

 presenting in general in the middle of the front a rudimentary 

 rostrum. Antennae inserted on two lines, and formed as in the 

 Shrimps, excepting only that the lamellar appendage of the second 

 pair is less. Mouth situated very near the base of these last, and 

 composed essentially of a labrum, a pair of mandibles furnished with 

 a palpiform stem, a lower lip, and two pairs of lamellar jaws. To 

 this family belong the genera Mysis, Cynthia, and Thytanopoda. 



Mysii. Body narrow, elongated. Carapace covering the anterior 

 extremity of the trunk as well as the greater part of the thorax, and 

 bent down on each side so as to apply itself against the base of the 

 feet. It ia free laterally, and does not adhere to the last rings of the 

 thorax ; anteriorly it is narrowed considerably, and terminates by a 

 small flattened and very short rostrum ; its posterior border is deeply 

 notched. Eyes large, short, and with their base hidden under the 

 anterior part of the carapace. Internal antennae inserted below the 

 eyes, near the median line; peduncle of the same form as in the 

 Shrimps, and carrying at its extremity two multiarticulate and rather 

 long filaments. The second pair of antenna; inserted below the pre- 

 ceding, and equally directed forwards ; the first joint of their peduncle 

 gives origin to a very elongated lamellar appendage, which is ciliated 

 on the internal border that covers the base of those organs, as in the 

 Shrimps. The two succeeding joints of the peduncle are slender and 

 cylindrical, and the terminal filament ia filiform, multiarticulate, and 

 longer than the upper antennae. 



There is no vestige of branchiae, either at the vault of the sides or 

 at the base of the feet, or at the lower surface of the abdomen, and 

 the only appendage which would seem to be modified in its structure 

 go as to become more proper than the rest of the body to fulfil the 

 functions of an organ of respiration, is the flagrum of the first pair of 

 jaw-feet, whose disposition, for the rest, is nearly the same as in a 

 great number of crustaceans provided with branchiae. 



On account of their peculiar appearance, the species of this genus 

 have been called Opossum Shrimps. The pouch which contains their 

 eggs, and which have secured for them this name, is thus described 

 by Mr. J. V. Thompson : " Attached to the base of each of the inner 

 divisions of the two posterior pairs of feet in the female, is a large 

 concave scale, strongly pectinate in front, of which the posterior is 

 the outermost, largest, and most concave, lapping considerably over 

 the anterior scale, so as to admit of a considerable extension of the 

 size of the pouch which they form by meeting each other in front, in 

 order to accommodate its capacity to the growth of the ova and young 

 brood. In the male, in place of the valvular pouch of the female, we 

 perceive attached to the inner part of the last pair of feet only, a 

 single small hollow scale on each side, ciliate in front, and provided 

 with a marginal row of slender hooks at the apex ; these are probably 

 an appendage of the male organs, which have a similar situation in 

 the Shrimps." 



Within this pouch in the female, the eggs, or rather embryoes, 

 Mr. Thompson informs us, are received when excluded from the 

 ovarium, and enveloped in a mucous or eubgelatinoug secretion, and 

 gradually developed without any visible attachment to the parent. 

 " The ova when first received into the pouch are considerably more 

 advanced than those of the Shrimps, Crabs, &c., on their first expul- 

 sion, and by no means so numerous, a circumstance more than com- 

 pensated by the rapidity with which one brood succeeds another 

 during the whole of the spring and summer months. The number of 

 broods produced by one individual, aa well aa the time occupied in 

 their evolution, have not been determined ; but the changes which 

 the embryo .undergoes ia configuration are sufficiently obvious. In 

 the present inatance these cannot be considered aa metamorphoses, 

 but limply a gradual development of parts; hence the Schizopoda may 

 be regirded aa one exception to the Crustaceans undergoing trans- 



formations, another character by which they are separable from the 

 true Shrimps, &c. The first change which is perceptible in the ova 

 after their reception into the maternal pouch is a slight elongation at 

 one end, and the appearance of two short members on each side ; 

 this elongation, which proves to be the tail, increasing in length, 

 shorly after becomes forked at the end, accompanied by a proportional 

 growth in the four lateral members, and which are the rudiments of 

 two pairs of antennae in the perfect animal ; the embryo going on thus 

 with a progressional development from day to day, begins to assume 

 a more complete form, and an approximation to that of the parent, in 

 which stages the divisions of the abdomen, the tail, the pedunculate 

 eyes, and the various members are sufficiently distinct ; a still more 

 close resemblance to the perfect animal is attained before the young 

 are finally excluded, which is effected by the parent spreading open 

 the valves of its pouch, when the whole brood emerge at once into the 

 ambient element, and, in most of the species, continue associated with 

 the community from which they sprang. The slight differences which 

 they now present (and which are necessary to be known in order to 

 preclude the possibility of their being mistaken for individuals of a 

 different species) affect only the inner rows of feet, the subabdominal 

 fins, the outer antennae, and the tail ; the first of these, in place of 

 the multiarticulate termination, have but one or two short joints and 

 a curved claw superadded to the end of the tibiae, and hence this 

 division of the limb ia shorter in proportion ; the subabdominal fins 

 consist only of a linear joint surmounted by a few bristly hairs ; the 

 outer antennae differ in no other respect than in the ciliated scale 

 which is attached to their base being shorter and less developed, as ia 

 also the brush of hair in the males ; the three intermediate scales of 

 the tail are proportionally shorter, but yet present the character 

 peculiar to the species in their form, indentations, and appendages, so 

 aa to testify the acuteness of Dr. Leach in having fixed upon this part 

 to distinguish the species from each other. What is further remark- 

 able in the embryoea is the way in which they are arranged within 

 the pouch from the moment they assume an elongated form ; their 

 heads being towards the breast of the mother, with the curvature of 

 the tail part suited to that of the outline of the pouch, and the large 

 size and blackness of their eyes." 



The species of Mysis swim freely in the sea in numerous troops, and 

 are particularly abundant in the north, where, according to Otho 

 Fabricius, they constitute a principal portion of the food of the 

 Whale-Bone Whales (Balcence). Captain James Ross, R.N., states 

 that Mysis flexuosus (Cancer flexuosus, MiilL), though but sparingly 

 found in the seas of Europe, inhabits some parts of the Arctic Oceau 

 in amazing numbers, and constitutes the principal food of the pro- 

 digious shoals of salmon that resort thither in the months of July 

 and August, and upon which the inhabitants of Boothia depend, in 

 great measure, for their winter store of provisions. He further 

 observes, that it is also the chief food of the whale, by which such a 

 prodigious quantity of fat is produced in the body of that immense 

 animal. 



M. Milne-Edwards divides the genus Mysis into the following 

 sections : 



1. Species which have the middle blade of the caudal fin 



bifurcated. 



M. spinulosus, Leach. It is the Praunus Jlexuosus, Leach ; Mysis 

 I,' iii-lii i, Thompson (' Zool. Res.'). It is found iu the British Channel 

 and the coasts of La Vende'e. (Milne-Edwards.) 



JUysis Fabricii, magnified. 



a, the last ring of its body, or its terminal fin ; b, base of a lateral antenna ; 

 c, base of an intermediate antenna ; d, one of the second pair of ja\v-fect j 

 c, one of the first pair. These parts highly magnified. (Dcsmarest.) 



2. Species which have the median blade of the caudal fin 



entire at the end. 



M. vv.lga.rw is common on the Irish coast. It abounds in the Leo, 

 even up to Cork, from the early part of spring to the approach of 

 winter, according to Mr. Thompson, who states that during the still 

 period of the tide at low water, they repose upon the mud and stonea 

 ut the bottom of the river, and, as tho tide rises, may be observed 



