No. 516] THE CUTICULA OF CESTODES 



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in origin to the cuticula has been very well shown by 

 Looss (1894), Young (1908) and other authors, who have 

 traced their development and growth. 



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, espe- 

 cially where these are very large, just as in the integu- 

 ment of insects a cuticular hair or scale is invariably 

 situated over the enlarged hypodermal cell which pro- 

 duces it. Nothing of the sort exists, however, in trema- 

 todes and cestodes. The subcuticular cells beneath the 

 hooks and spines do not differ in size, number or arrange- 

 ment from the adjacent cells, and in the monogenetie 

 trematodes, which are often provided with gigantic hooks, 

 no subcuticular cells at all are present. In the six-hooked 

 embryo of cestodes the hooks make their appearance in 

 the embryonic parenchyma, while there are as yet no 

 subcuticular cells present. The parenchyma is thus the 

 matrix of the hooks at this early stage of the animal's 

 existence. 



Another point of importance is the essential difference 

 in structure between the cu- 

 ticula of trematodes and ces- 

 todes and that of other worms 

 and of arthropods in which 

 the cuticula is the secretion 

 of an undoubted hypodermis. 

 In the former the character- 



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