1887.] 



ON CYCLESTHERIA HISLOPI. 



27 



Phyllopoda, as- also in the Cladocera. At this poiut the dorsal 

 edge exhibits a strong heel-shaped curve. its upper or anterior 

 part, which is quite smooth, running out in a line with the dorsal 

 edge of the trunk. Finally, to the soniewhat truncate extremity 

 of the tail, two exceedingly elongate and slender, slightly curved 

 claws, apparently corresponding to the caudal lamellæ in the 

 Branchipodidæ, are movably articulated, ha ving between them the 

 anal orifice. These claws, like the dorsal spines, are armed with 

 numerous small denticles arranged irregularly throughout their 

 w hole length posteriorly. At some distance from the spiniferous 

 part of the dorsal edge and running nearly parallel to it, is 

 seen a distinctly marked line, extending from the base of the ter- 

 minal claws to the setiferous knoblike projection mentioned above. 

 This line indicates the bottom af a rather deep and narrow fis- 

 sure, extending between the spined edges of the caudal plate and, 

 as it were, dividing it into two symmetrical laminæ. 



C. The inner Organs. 



a. The Nervaus System. 



The supraæsophageal or cerebral ganglion (Pl. III, fig. 5, g) 

 is located within the preoral part of the head, posterior to the 

 compound eye and immediately below the anterior part of the 

 intestine. It is rather large and of a somewhat irregular form, 

 but very difficult to examine minutely on account of its being 

 to a great extent concealed by the scape of the antennæ. 

 From the upper part of this ganglion, and somewhat in front, 

 the strong optic nerves originate. These nerves are not united, 

 but quite separate throughout their whole extent, each being 

 expanded at the end to a rounded ganglion, lying at a short 

 distance posterior to the eye and sending off to this organ 

 numerous fine nerve-fibres. The anterior corner of the cerebral 

 ganglion is exserted to a narrow point, applied against the poste- 

 rior angle of the ocellus. The antennular nerves, apparently 

 originating from the posterior part of the cerebral ganglion, may 

 be easily traced as a delicate stem running along the axis of 



