260 SUPPLEMENT 



five principal groups, of four each, corresponding to the base 

 of the first four feet, and of the external jaw-feet. Moreover, 

 one isolated branch is placed altogether in front, and fixed to 

 the second jaw-foot, while another equally isolated corresponds 

 to the last or fifth foot. These gills are compressed by 

 elongated, cartilaginous laminae, mobile, and attached one to 

 the basis of each foot, for the purpose of expressing the water. 

 These lamina) separate the groups of gills, and in each group 

 there is one of these gills, the most external, which is fixed to 

 the basis of the lamina, and like it, moveable ; the others, be- 

 ing adherent to the body itself, have no proper movement. 

 Two similar laminas, without gills at their base, are attached 

 to the most anterior jaw-feet, and to the last jaw properly 

 so called. 



The testa of the Crustacea also presents an anterior aper- 

 ture below its edge and on each side of the mouth, for the 

 issue of the water. 



In the Squillae the gills are visible, and can serve for loco- 

 motion : they are situated under the body and behind, to the 

 number of five pairs, annexed to some short fins, divided into 

 two lobes, and formed of membranaceous laminae, ciliated on 

 their edges. It is at the root of the external lobe of these fins, 

 and at its internal edge, that the gill, which is very compli- 

 cated, and which at first sight resembles a thick pencil, is at- 

 tached, M. Cuvier, who was the first to observe this organ, 

 describes it thus : " The gill is at first formed of a conical pe- 

 duncle, composed of two vessels. There proceeds from it a 

 range of cylindrical tubes, which go on diminishing from the 

 base of this peduncle to its point, similar to the arrangement 

 of the pipes of an organ. Each of these is curved, and forms 

 a long conical and flexible tail, which itself bears a very nu- 

 merous range of long floating filaments, like lashes. Each 

 filament contains two vessels, each tail and each tube two 

 likewise, as does the general peduncle. 



