REPORT ON THE ISOPODA. 19 



Serolis schijthei aud Serolis latifrons, presents some differences. Fig. 4 is a drawing of 

 the masticatory stomach of Serolis schythei, which is entirely similar to that of Serolis 

 latifrons; the chief difference from Serolis hromleyana is that the lateral ossicle (fig. 4, 1) 

 is furnished upon the upper surface with short spines in addition to the delicate hairs 

 which clotlie its lower surface. The outermost of the three pairs of ossicles which form 

 the pyloric half of the stomach is also more extensive, and bears the ribbed lateral plates 

 {RP, LP) upon the anterior edge. 



At the junction of the masticatory stomach with the intestine are four caeca which 

 are long and coiled in Serolis cornuta (PI. X. fig. 2); in a specimen of Serolis 

 necBra that I dissected there were also four cseca, two situated beneath the gut, and con- 

 siderably shorter than the other two which lay along the outer margin. 



From the masticatory stomach arises the intestine, which is at first wide but gradually 

 narrows towards the rectum ; the latter commences at about the level of the fifth 

 thoracic segment, and is separated off from the intestine by an incomplete circular valve ; 

 the anus is an oval aperture ou the ventral surface of the body between the attachments 

 of the gill plates. The intestine as well as the rectum is provided internally with a 

 series of lonoitudinal oiandular folds. 



In a member of small specimens of Serolis latifrons mounted on slides in Canada 

 balsam the alimentary canal was distinctly visible ; between the wdde anterior portion 

 of the intestine aud the rectum, which is half its diameter, is a narrow portion of the gut, 

 measuring at its commencement rather less than one half of the diameter of the rectum, 

 and then becoming slightly wider as it approaches the latter. 



Nervous System. — The nervous system of Serolis paradoxa is figured in Packard's 

 Zoology ; ^ Studer has also given a figure and description of the nervous system of 

 Serolis latifrons; the former of these two figures appears to represent more strikingly 

 the concentration of the posterior ganglia into a nervous mass where the commissures 

 and connectives between the several ganglia are lost. 



I have studied the nervous system of the genus in two species — in young examples 

 of Serolis earinata by means of sections and by simple inspection of the entire animal 

 mounted in glycerin ; in Serolis necera by dissection. 



The nervous system of both these species, as in other Crustacea, shows a relation to 

 the segmentation of the body ; the fusion of the anterior segments is accompanied by a 

 fusion of their ganglia, and the same thing has taken place in the posterior region of the 

 body. On PI. II. fig. 1 4 is represented the nervous system of Serolis septemcarinata ; 

 the drawing has been made from a specimen mounted on a slide, but the number of the 

 ganglia has been checked by comparison with a complete series of longitudinal sections 

 through an animal of the same size. 



The cerebral ganglia are very large, and present the appearance of being composed 



1 Zoology, Packard, iud ed., New York, 18S0, p. 307. 



