POLYCLAD TURBELLAKIA. 131 



there are a number of scattered eye-spots about equal in size to those lying at the 

 base of the tentacles, over the brain. In addition there are very numerous smaller 

 spots on the margin. These do not extend completely round the body, but only 

 about halfway along the margin on either side. They form anteriorly two or three 

 irregular rows. 



Genital Organs. The ovaries are dorsal. The most striking peculiarity of this 

 species is found in connection with the hinder ends of the vasa deferentia just before 

 they enter the vesicula seminalis. They are provided in that neighbourhood with 

 verv thick muscular walls, which are quite as thick as the walls of the vesicula 

 seminalis itself. The prostate is divided into a number of parallel chambers, its walls 

 are formed of muscle-fibres which have a very definite " lattice-work" appearance. 



In one specimen the penis was completely everted. The vagina opens into the 

 same wide shallow depression as that into which the antrum masculinum passes. 



This species may be defined as a Stylochus with an incomplete series of marginal 

 eye-spots, with the ovaries occupying a dorsal position, and with the genital 

 apertures closely approximated. The prostate is divided into a number of parallel 

 chambers, and the lower ends of the vasa deferentia are highly muscular. 



Stylochocestus, n. gen. 



Body elongated, with neither marginal nor tentacle eye-spots. Buccal aperture 

 sub-central. 



Prostate gland large, provided with a short duct which joins the vesicular duct at 

 the base of the penis. Vagina without accessory vesicle. 



Stylochocestus gracilis, n. sp. Plate, fig. 7. 



Several specimens (Gardiner). 



Measurements. Length, about 14 millims. ; breadth, about 3 millims. Male 

 aperture 4 "5 millims. from hinder end of body; female aperture - 5 millim. behind 

 male. Buccal opening sub-median. 



I have no information as to the coloration of this species during life. 



The eye-spots are arranged in two parallel rows over the brain. 



Body-wall. The epidermis of the dorsal surface contains rather large rhabdites, 

 and in places also pseudorhabdites equal in length to the rhabdites, but much 

 broader and rather irregular in outline. These are both absent from the ventral 

 surface, except towards the margin of the body, whilst the ventral epithelium is 

 flatter. 



The basement membrane is thin, but stains deeply. The muscles lying immediately 

 below it on the dorsal side are first a longitudinal layer, then a double diagonal layer, 

 and lastly a circular layer. On the ventral side this is again succeeded by an inner 

 longitudinal layer. 



The gut branches do not anastomose. 



