294 



F. F. LAIDLAW. 



approximate more closely to the yolk-glands of the Triclads than to any structure previously 

 known amongst the Polyclads. It is possible, however, that they are connected with the cell- 

 like bodies found in the uterine vesicles as described above. 



Male apparatus. The vasa deferentia are crowded with spermatozoa. They enter the 

 walls of the penis some little distance behind its anterior end, narrowing as they do so. For 

 the first third of its length its lumen is lined by glandular cells, and filled with a coarsely 

 granular secretion (see Fig. 66). For the rest of its length it has a cubical ciliated epi- 

 thelium, as also has the antrum masculinum. The wall of the penis is composed chiefly of 

 circular fibres, interspersed with a few radial. The antrum becomes extremely narrow as it 

 approaches the gonopore, and the latter is correspondingly minute. 



Fig. 66. Section across the base of the penis of Pericelis byerleyana. 

 ^e. = penis, pr. c. = glandular cells, v. d. =vasa deferentia, d.e. = va,s deferens entering penis. 



Leaving the specialized Prosthiostonium out of account I believe that all other Cotylea save 

 Anonymus have a special muscular prostatic organ connected with the penis by a short duct. 

 Consequently Pericelis is more nearly related to Anonymus in the structure of the terminal 

 parts of this organ than to the rest of the Cotylea. 



V. Family P.SEUDOCERIDAE. 



7. Thysanozoon plehni, sp. n. (PL XIV. fig. 7, and PL XV. fig. 19). 



Three specimens " from the reef-flat " Minikoi, with " brown to slate-black papillae." 



Total length about 23 mm. Total breadth about 17 mm. ' Mouth opening ' about 5 mm. 

 behind the anterior margin. </ aperture 4 mm. behind the ' mouth.' $ aperture 1 mm. behind 

 the male. Sucker 2 mm. behind the female aperture. 



The ground-colour of the body in the spirit specimen is a dull pale yellow. On the 

 •dorsal surface lie a considerable number of black, rather pointed papillae; the small marginal 

 tentacles are also black. Brain-eyes in a single small cluster; tentacle-eyes an-anged along 

 the anterior side of the tentacles (Fig. 67). 



The muscle-layers of the body-wall are but feebly developed. The dorsal papillae contain 

 no gut diverticula, only a loose parenchyma. Their epithelium is composed of very long, 

 columnar cells, loosely connected with each other, containing clusters of rhabdites which vary 

 in length from -01 to -0275 mm. In addition to the rhabdites the epithelium of the papillae 

 secretes a small number of pseudorhabdites, bodies of about the same length as the larger 

 rhabdites, but two or three times as broad and of a finely granular texture. They occur 

 nowhere save on the papillae (PI. XV. fig. 19). At the tip of each papilla is a small 



