78 CRUSTACEA. 



for natation, or are fin-feet. Their shell is divided into 

 two portions, the anterior of which supports the eyes and in- 

 termediate antennse, or composes the head, without giving 

 origin to the foot-jaws. These organs, as well as the four 

 anterior feet, are frequently approximated to the mouth on 

 two lines that converge inferiorly, and hence the denomina- 

 tion of Stomapoda affixed to this order. Judging by the 

 Squillse, the most remarkable genus of this order, and the only 

 one hitherto studied, the heart is elongated, and similar to a 

 large vessel. It extends along the whole length of the back, 

 rests upon the liver and intestinal canal, and terminates poste- 

 riorly and near the anus, in a point. Its parietes are thin, 

 transparent, and almost membranous. From its anterior ex- 

 tremity, placed immediately behind the stomach, arise three 

 principal arteries, the mediate of which the ophthalmic 

 giving off several branches on each side, is more particularly 

 directed to the eyes and intermediate antennae, and the two 

 lateral ones the antennaries pass over the sides of the sto- 

 mach and are lost in the muscles of the mouth and of the ex- 

 ternal antennae. No artery arises from the superior surface 

 of the heart, but a great many issue from its two sides, each 

 pair of which, as it appears to us, corresponds to a particular 

 segment of the body, commencing with the foot-jaws, whether 

 these segments be external, or concealed by the shell, and 

 even very small as is the case with those that are anterior. 

 On a level with the first five abdominal annuli, or those to 

 which the natatory appendages and the branchiae are attached, 

 this superior surface of the heart receives, near the median 

 line, five pairs of vessels a pair to each segment proceeding 

 from these latter organs, and which, according to Messrs 

 Audquin and Milne Edwards, are analogous to the branchio- 

 cardiacs of the Decapoda. A central canal (1 ) situated under 



(1) See our general observations on the Macroura. Neither this vessel nor the 

 venous sinuses have been observed in the subsequent orders; but the heart pre- 

 serves the same elongated form, and presents similar anterior arteries. From its 

 sides also arise other arteries corresponding to the articulations of the body. In 

 addition to the pre-cited Memoir, see the Lecons d'Anatomie Comparee of the 

 Baron Cuvier. 



