No. 510] THE CUTICULA OF CESTODE8 



725 



worms has affected all their organs and tissues in so 

 marked a degree. 



The function of these cells is a much more difficult 

 matter to determine, and two diametrically opposed 

 classes of views have been expressed concerning it. Ac- 

 cording to one of these, they form a specialized tissue 

 with either a secretory or an absorptive function. Ac- 

 cording to the other, they are an unspecialized embryonic 

 tissue, which has no direct physiological relation to the 

 other structures of the body. 



If the almost unanimous decision of all the investiga- 

 tors who have studied trematodes and cestodes is to be 

 accepted, the subcuticular cells are glandular or secretory 

 in function and, as we have seen, the cuticula is the prod- 

 uct of their secretion. Some years ago (1898) I sug- 

 gested that they (as well as the single-celled glands) 

 may secrete, not the cuticula itself, but some substance 

 which tends to render the cuticula immune to the disin- 

 tegrating effects of the body-fluids of the host in which 

 they pass their lives. That the cuticula of endoparasitic 

 trematodes and of cestodes does possess some special 

 means of protecting itself and the other tissues of the 

 worms seems certain. Looss, for instance, has taken Dis- 

 tomum tereticolle from the stomach of the pike, where 

 the worm was pressed tightly against the stomach-wall by 

 large masses of actively digesting food. Something in this 

 case must have prevented the worm from being digested, 

 too. This special means of defense is not to be looked 

 for in the physical structure of the cuticula itself, which is 

 usually soft and easily injured, but in some chemical sub- 

 stance which neutralizes the action of the juices of the 

 host. It is possible that the subcuticular cells secrete 

 some such substance, especially as the ectoparasitic 

 trematodes, which are in most cases either not sur- 

 rounded by the tissues of the host or are only partially so, 

 do not, as we have seen, possess these cells. 



What the reaction of these secretions would be must 

 depend upon the nature of the fluid in which the worm is 



