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THE AMERICAN NATURALIST [Vol. XLII1 



typical arthropod or worm cuticula is never present (al- 

 though it may be made up of several layers), but, on the 

 other hand, a fundamentally fibrous structure can often 

 be demonstrated with perfect clearness, the fibers being 

 sometimes in very evident connection with the paren- 

 chyma beneath and a portion of it (Figs. 8 and 9). 



In fact, the so-called ducts of the subcuticular cells are 

 nothing more nor less than the fibrous projections of 

 these cells which, together with similar projections of the 

 parenchyma cells themselves, sometimes extend to, and 

 occasionally, especially in young animals, into the cutic- 

 ula. In certain cases these fibers may arrange them- 

 selves so as to form a series of vertical strands in the 

 cuticula, passing between its inner and outer surfaces, 

 and have been interpreted in the past to be pore-canals, 

 structures which are probably not present in any trema- 

 todes or cestodes. Whatever toughness of texture the 

 cuticula of these worms possesses is probably due to this 

 fundamentally fibrous or leathery structure. The cutic- 

 ula is further exceedingly elastic; it is often very soft 

 or even semi-fluid and easily destroyed in caustic potash 

 and as the result of maceration; and it is never moulted 

 as a whole nor can it be usually separated from the tissues 

 beneath-all of which characteristics are foreign to the 

 cuticula of other worms and of arthropods. 



The differences between an undoubted hypodermis 

 and the subcuticular cells are also fundamental and very 

 striking, and are not satisfactorily explained by Bloch- 

 niann, who compares with them the hvpodermal cells of 

 Hirudo and other animals which may be more or less 

 separated from one another by parenchyma and other 

 tissues. The origin of these cells forms the embryonic 

 parenchyma, as shown clearly bv many authors, and the 

 frequent anastomosing of them with one another and with 

 the Burronnding parenchyma, are characters which no 



I 1 ia true thai there is a strong superficial resemblance 

 between the subcuticular cells in cestodes— but seldom or 



