1887.] 



ON CYCLESTHEEIA HISLOPI. 



43 



Crustacea, whereas the other parts are homologous with the main 

 stem, or endopodite, and the natatory branch, or exopodite. Thus, 

 in analogy with other Crustacea, only the first of these three 

 principal parts of the legs. representing the epipodite, should be 

 regarded as the true respiratory organ. But the comparatively 

 small size and simple structure of this part would not seem 

 to corroborate such an assumption; most naturalists therefore 

 regard the whole leg as devoted to this function. and more 

 especially the greatly developed exopodite, the delicate structure 

 of which would also seem to render it highly suitable for respira- 

 tory purposes. There is, however, another part of the body, at 

 least in the present group of Phyllopoda, that apparently 

 can lay claim to a true respiratory function, and to which 

 such a function has been ascribed by several authors. We 

 allude to the valves of the shell, which, as above stated. receive 

 a very considerable quantity of blood, and the inner delicate 

 coating of which would seem highly calculated to produce an 

 exchange of gases with the water. The necessary renewal of 

 the water is effected by the well-nigh uninterrupted movements 

 of the legs, whereby a continual current is produced within the 

 shell, bathing not only the legs themselves but also the inner 

 coating of the valves. 



F. Seere tion. 



The only organ to which such a function has been attributed, 

 is the so-called shell-gland. Its structure would seem to be 

 glandular, but of what nature the secretion is, and in what 

 manner performed, has not yet been ascertained satisfactorily. 

 Some naturalists opine that this peculiar organ secretes the 

 material of which the shell is built up, but it is far from 

 evident that such is its real function. On examining the organ 

 closer, I have failed to detect any secreting orifice, the whole 

 organ appearing to constitute a convoluted canal or duct recurring 

 in itself 



