Archive image from page 794 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana01todd Year: 1836 CRUSTACEA. 779 conformation; they appear like a vesicular or foliaceous expansion, of an extremely soft tex- ture, which is attached to the inner edge of the base of the thoracic extremities; their dimensions generally increase from before back- wards, and the last pair of thoracic extremities is not furnished with any : their total number varies from eight to twelve. These organs, suspended under the thorax, float in the ambient fluid, and the water in contac
Archive image from page 794 of The cyclopædia of anatomy and. The cyclopædia of anatomy and physiology cyclopdiaofana01todd Year: 1836 CRUSTACEA. 779 conformation; they appear like a vesicular or foliaceous expansion, of an extremely soft tex- ture, which is attached to the inner edge of the base of the thoracic extremities; their dimensions generally increase from before back- wards, and the last pair of thoracic extremities is not furnished with any : their total number varies from eight to twelve. These organs, suspended under the thorax, float in the ambient fluid, and the water in contact with their surface is incessantly renovated by means of the motions performed by the abdominal extremities of the animal, motions which occa- sion a rapid current from behind forwards along the ventral aspect of the body. In the Lremodipoda, the parts which perform the office of branchiae are vesicular bodies formed by the flabelliform appendage of a certain number of the pairs of thoracic extre- mities. In the Isopoda, finally, the locomotory extremities no longer serve for respiration, the function being committed to the five first pairs of abdominal extremities which are entirely devoted to it and cease to have any other uses. These extremities, which are designated under the name of false branchial limbs, consist of a cylindrical articulation, supporting two folia- ceous, soft membranous laminae, vascular in a greater or less degree; frequently, too, we perceive on their inner side a small appendage, which may be regarded as analogous to the femur or stem of the other extremities, whilst the two laminae, of which mention has just been made, appear to represent the palp and the flabellum. In the greater number of Iso- poda these organs are completely exterior, but in several (such as the Idotea) the last ring Fig. 423. Fig. 424. Respiratory apparatus of the Idotea. of the abdomen supplies them with a cavity, the entrance to which is closed by valves which constitute t
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