\Q Alt. 3. — T. Kabuiaki : 



the Turbellarian epidermis is homologous with the cuticular wall 

 of the Trematodes and Cestodes, as pointed out by Lönkberg (40), 

 Ziegler (77) and others. Further, the fact, which will be set 

 forth in the paragraph concerning the atrium, probably affords a 

 strong support for this view. 



Rhabdltes. — As is well known, the epidermal cells contain 

 numerous rhabdites as a peculiar content, the rhabdites lying near 

 the free surface of the cells and chiefly occupying the distal half. 

 Some of the rhabdites may sometimes reacli the basement mem- 

 brane. Usually their major axis is approximately perpendicular 

 to the surface and nearly parallel to one another, but the3" may some- 

 times assume an}^ angle with one another. In St. trigonocephala 

 they are found in a very small number, evidently situated between 

 the epidermal cells. In Pr. lactea and Ect. Umuli the epiderniis is 

 full of rhabdites usually within, and rarely between, the cells. 

 Generally the rhabdites occur in great abundance, so that the 

 epidermis appears at one glance to be composed of them, on the 

 dorsal surface, up to the lateral margin of the body, where the 

 body-glands open to the exterior, and where they abruptly cease. 

 They are, liowever, altogether absent in the sensory regions, and 

 become remarkably fewer in number on the ventral surface, dis- 

 appearing altogether around the genital aperture. 



As stated above, the epidermis is full of the rhabdites which 

 are all of one kind, but vary in size. The variations occur wher- 

 ever the rhabdites are found. Generally speaking, however, there 

 is an interesting correlation between the thickness of the epider- 

 mis and the size of them, as mentioned by Woodworth (74). 

 The rhabdites are invariably longer on the dorsal than on the 

 ventral side, their length measuring on the average in Pr. lactea 6 

 fji dorsally by 4 fi ventrally, and in botli St. trigonocephala and 

 Ect. llmidi 4 {j- dorsally b}' 3 p- ventrally. Each is generally of a 

 slightly curved fusiform shape, bluntly pointed at both ends, and, 

 more or less slender in the, latter two species than in the former. 

 In general, they are deepl}^ stainable Avith borax-carmine, and 

 when stained with haematox^^lin-eosin, the}' take on a violet 

 colour. They are of a perfect! 3^ homogeneous and strongly reflec- 



