96 



that Dr. A. Dohrn has described and figured under Cuma a rather complicated 

 system of arterial vessels issuing on each side from a single stem originating 

 from the heart. Through this system, the blood is said to be carried both 

 backwards and forwards, the vessels, especially in the walls of the carapace, 

 exhibiting abundant ramifications. There can be no doubt that this statement is 

 based upon direct observation ; but I suspect that the existence of these vessels 

 has merely been assumed from the course of the blood-corpuscles, which indeed 

 circulate through the body with great regularity, though not in my opinion, 

 enclosed in any distinctly defined vessels. 



3. Renal System. 



Under this head, I may mention a pair of problematic organs occurring 

 in all Cumacea, one on each side of the heart, and easily observable owing to 

 their opaque whitish colour (see PI. LXV LXVI1I. fig. 1. n). These organs 

 have the form of rather short, somewhat curved tubes, exhibiting several rounded 

 lobules and slightly diminishing in thickness behind (see PI. LXVI. fig. 6). They 

 contain a uniform, finely granular mass without any cellular elements (see fig. 7), 

 the granules, under a high magnifying power, exhibiting a somewhat irregularly 

 angular form, and thus resembling calcareous concretions. I have failed to detect 

 any excretory duct, and indeed, I am of opinion that strictly speaking these 

 organs are not secretory, but that they merely serve as storing places for some 

 unserviceable matter secreted from the blood. I long ago 1 ) described a pair 

 of undoubtedly homologous organs in Ascllus aquaticus, where they likewise occur 

 on each side of the heart, and at that occasion I expressed a similar opinion 

 as to the significance of these organs. 



4. Nervous System. 



As in other Crustacea, the central parts of the nervous system consist 

 (see PL LXVI, fig. 2) of the cephalic ganglion situated in front dorsally, and 

 the nervous chord running along the ventral side of the body. The latter is 

 composed of a series of 16 ganglia connected by double commissures. Of these 

 ganglia the first 10 belong to the anterior division of the body, and are much 

 larger than the remaining 6 caudal ones, which, with the exception of the last, 

 are very slight, almost obsolete. All the ganglia consist of 2 symmetrical parts, 



1 ) Crustaces cl'eau douce de Norveofe. 



