ON CRUSTACEA. 
201 
The amphipod 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, Lamodipoda) 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 asCymotlioe, 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 limuhe have, under the 
second part of their testa, five large transverse laminae 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 daplinis, 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 
