No. 516] THE CUTICULA OF CE ST ODES 



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muscle strands and no embryonic cells persist; hence no 

 subcuticular cells are present. 



Originally these indifferent cells lie around all of the 

 growing organs, especially the genital organs, as well as 

 near the periphery of the body. But in the course of the 

 growth of the worm all disappear except those near the 

 periphery, which become the subcuticular cells and may 

 remain throughout life, giving rise to new parenchyma 

 cells, and also to muscle strands and to flame-cells. In 

 old digenetic trematodes, however, they may also disap- 

 pear (Lander, Maclaren). Looss compares these cells 

 to the cambium of plants, which is also an indifferent 

 tissue which gives rise to certain specialized tissues 

 throughout the life of the plant. 



The only authors who have fully subscribed to this 

 theory, so far as I know, are Xickerson (1894) and Staf- 

 ford (1896), who support it by observations drawn from 

 the study of Sichocotyle and Aspidogaster, respectively, 

 although Schuberg (1894), Lander (1904), Balss (1908),. 

 Young (1908) and others have declared in favor of the 

 parenchymatous origin of the subcuticular cells. 



That so few have done so is probably due, as I have al- 

 ready indicated, to the fact that the belief in the glandular 

 nature of the cells in question is so firmly fixed in the 

 minds of helminthologists as to have axiomatic force. 

 But it must never be forgotten, notwithstanding this cir- 

 cumstance, that this particular function has never been 

 proven for these cells. No one has yet seen them produce 

 a secretion and the supposed ducts that are seen in con- 

 nection with them in some, although by no means in all 

 species, and the possession of which is perhaps the prin- 

 cipal proof which has been brought of their glandular 

 nature, are not ducts at all. In contrast to them we might 

 indeed place the single-celled glands, whose ducts are al- 

 wavs perfectly plain and whose secretion can be seen. It 

 must also be remembered that neither Leuckart nor 

 Looss, each of whom, it will be generally conceded, has 

 surpassed all contemporary investigators in his knowl- 



