OA' CRUSTACEA. 261 



The ampliipod Crustacea (Gammarus) are provided with 

 vesicular appendages, placed at the interior base of the feet, 

 with the exception of those of the anterior pair, and which 

 have been considered as gills. Among the isopods, some, 

 such as Leptomera (which is placed by M. Latreille in his 

 fourth order, Lcemodipoda) and some others, have, as apparent 

 or presumed, respiratory organs, only some very soft vesicular 

 bodies, sometimes six in number, and situated at each side, 

 on the second, third, and fourth segments, at the external base 

 of the feet, which are attached there ; sometimes there are but 

 four of them, which are annexed to as many true or false 

 feet of the second and third segment, or to their place, if 

 these segments are absolutely destitute of locomotive organs. 

 Others, such as typhis, &c. have gills under the tail, always 

 naked, and in the form of stems, more or less complicated. 

 Others, in fine, such as Cymothoe, Asellus, Oniscus, &c. have 

 gills under the tail, either free, and in the form of vascular 

 scales or membranaceous pouches, sometimes naked, some- 

 times covered by plates ; or enclosed in scales. Among these 

 last are those Crustacea which can only respire the atmosphe- 

 ric air directly, and not through the watery medium. 



The sub-class of entomostraca presents very numerous vari- 

 ations in the respiratory organs. The limulse have, under the 

 second part of their testa, five large transverse laminoe or jaw- 

 feet united at their base, and bearing at their posterior face a 

 great number of fine leaflets, piled up, which are the gills. 

 Similar laminae are remarked under the second part of the 

 body of the caligi, and probably likewise cover some bran- 

 chial leaflets. In daphnis, the ten feet are composed of many 

 shortened articulations, and the last eight are provided, among 

 these articulations, with a membranaceous lamina, ciliated on 

 its edges, and which serves for respiration. It was for a long- 

 time believed, that in Cypris the organs of this function were 



