1911] Watson: The Genus Gyrocotyle. 419 



of interest to students of the phylum has been found; this will 

 be briefly discussed before proceeding to consider the main prob- 

 lems of orientation. 



I. CUTICULA. 



The question of ectodermal origin of the "cuticula" or limit- 

 ing membrane of the body, and the significance of the "sub- 

 cuticular cells ' ' in the trematodes and cestodes has been recently 

 reviewed by Professor Pratt (1909). Blochmann's theory, re- 

 garding the subcuticular cells as a sunken epithelial layer, and 

 the limiting membrane as a true cuticula, such as is found in 

 arthropods and annelids, Pratt considers completely discredited 

 by various pieces of embryological and morphological evidence. 

 He considers the "cuticula" to be nothing but a closely matted 

 layer of parenchyma fibres, from which the nuclei have dis- 

 appeared. The observations made on Gyrocotyle seem to bear 

 out this view of the limiting membrane. Of particular interest 

 are the conditions of the vagina, receptaculum seminis and 

 uterus. Here the lining of these ducts is in direct continuity 

 with the cuticula at their openings ; there is a gradual transition 

 from this cuticular lining to one of comparatively loose-matted 

 fibres and indefinite boundaries, containing unmistakable paren- 

 chyma nuclei and passing on its inner surface indistinguishably 

 into a typical parenchymatous net in which lie muscle fibres. 

 This same transition can be seen on the inner surface of the folds 

 of the posterior rosette. Furthermore, nowhere in Gyrocotyle 

 have I found a definite layer of epithelial cells. Such tissue, 

 described by Lonnberg for the ducts of the reproductive system, 

 resolves itself in favorable preparations and under high magni- 

 fication into the dense parenchymatous layer, fibrillated and 

 without cell-walls, above described. 



One statement made by Pratt in support of this view of the 

 cuticula as not associated with the subcuticular cells is not borne 

 out by conditions in Gyrocotyle. He says: "If now the cuticula 

 is the product of the underlying subcuticular cells, we should 

 expect to find some special development of them beneath the 

 hooks and spines, especially where these are very large, just as 

 in the integument of insects a cuticular hair or scale is invariably 



