On Stichocotyle nephropis Cunningham, a parasite of tlie American lobster. 453 



pretty generally discarded. If this theory were correct, we might 

 expect to Hud that in an animal which is increasing in length by 

 growth at the posterior end, as is the case in Stichocotyle, there would 

 still be present in the growing region a portion of the epidermis to 

 secrete the covering of this newly formed part of the body. No trace 

 of such epidermal cells can be detected in Stichocotyle, and yet the 

 external layer is everywhere present, though somewhat thinner in this 

 region than in the older portion of the body. 



Secondly, the theory that certain of the cells underlying the mus- 

 culature of the body wall are gland cells and secrete the material of 

 whicli the outer layer is made up, has been recently maintained by 

 BiiANDiiS ('92). He believes that in a considerable number of species 

 he has been able to distinguish such cells and to trace the ducts 

 from them through the musculature into the outer layer, where they 

 terminate. I feel very confident that in Stichocotyle there are no such 

 glandular cells to be distinguished. I have tried a considerable num- 

 ber of diiierent stains, including the haematoxylin dyes of Kleinen- 

 berg, BoEHMER, Ehrlich and Heidenhain ; also lithium picro-carmine, 

 borax carmine, alum carmine, Czokor's cochineal, Mayer's HCl-carmine 

 besides several aniline dyes, and in no case can processes of cells be 

 detected extending through the muscular layer into or toward the 

 outer body layer, as described and figured by Brandes for a large 

 number of digenetic Trematodes. It is therefore impossible to accept 

 this view as a satisfactory explanation of the conditions found in 

 Stichocotyle, even though it is in the highest degree improbable that 

 the layer in question has in this case a different origin from that 

 which obtains in all other Trematodes. 



Thirdly, the theory that the outer layer is a metamorphosed 

 epidermis from which nuclei and cell-boundaries have disappeared, 

 has gained a good deal of acceptance during recent years. This view 

 derives most of its support from the fact that several observers have 

 reported finding traces of degenerate nuclei in the external layer. 

 This is the theory which Monticelli has adopted and applied in 

 describing the outer layer of Cotylogaster , though he finds in that 

 form little evidence to support this conception. The latest evidence 

 which he has put forth in support of this view (Monticelli, '93) I 

 have unfortunately not been able to consult. The paper has come 

 to my knowledge only through the review published in Zool. Cen- 

 tralbl., V. 1, p, IG. It would appear from this review that no new 

 kind of evidence has been brought forward, but that M(tNTicELLi finds 



