8 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



substance serving to render the cuticula immune from the disintegrating 

 action of the body fluids of the host. He states that these cells are 

 lacking in the appendix ; but in Hemiurus crenatus the subcuticular cells 

 are as abundant in the appendix as in any other region of the body. 



In Hemiurus crenatus the subcuticular cells give no indication what- 

 ever of being glandular. I find no traces of ducts, their cytoplasm is 

 homogeneous or very finely granular, and they commonly form syncytia 

 rather than distinct cells. I have, hovirever, been unable to find any cells 

 which I could identify as the Hautdriisen, or dermal glands, commonly 

 described in trematodes. I believe the subcuticular cells of this species 

 are primitive, undifferentiated cells, a very large number of vrhich persist 

 throughout the life of the worm. It seems probable that all the cells or 

 nuclei of each group arise from the division of a single cell or its nucleus ; 

 and although none were observed in process of division, there is nothing 

 in their appearance to suggest that they have lost the power of division. 

 Thus the subcuticular cells, as Looss ('93) suggests, correspond anatom- 

 ically and physiologically to the cambium of plants. As will be suggested 

 later, I think that they probably give rise to myoblasts, but I have found 

 no indications either of their degeneration, of their development into 

 vesicular parenchyma, or of their conversion into gland cells. 



The oval and spindle-shaped granular cells of this layer are probably 

 cells in process of development into parenchyme muscle fibres. The 

 development of these muscle fibres from oval cells lying in the par- 

 enchyma has been observed by Poirier ('85) in young specimens of 

 Distomum clavatum and D. verrucosum. He finds all stages from the 

 oval cells to the almost entirely formed muscle fibre. The nucleus and 

 cytoplasmic portion of the cell are surrounded by the contractile portion, 

 which he describes as being formed by a thickening of the wall of the 

 cell. According to Poirier, both granular protoplasm and nucleus 

 entirely disappear, though there remains for a long time, and even in 

 adult animals, a central core diflfering noticeably in appearance from the 

 peripheral portion. 



The parenchyme muscle fibres described by Mace ('82) and those 

 described by Stafford ('96). in which the body of the muscle cell lies on 

 one side of the contractile fibre, suggests another method of development 

 of parenchyme muscle fibres, which resembles the supposed process of 

 development of the muscles of the body wall, in that the body of the 

 cell remains external to its contractile portion. 



As to the source of these myoblasts, I am inclined to believe that they 

 are derived from the subcuticular cells, which, as stated above, I believe 



