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THE AMERICAN NATURALIST [Vol. XLIII 



of the very young larva is composed essentially of fibers 

 and nuclei closely bound together (Fig. 11) and that the 

 adult cuticula may be in direct connection with the sub- 

 jacent parenchyma and contain some of its nuclei (Fig. 

 9). It is conceivable, however, notwithstanding these 

 facts, that foreign objects such as particles of coagulated 

 blood, which often adheres to the outer surface of these 

 worms, could be forced into the soft cuticula from the 

 outside as a result of the pressure to which the worms are 

 often subjected in their natural environment, or perhaps 

 in the compressor or under the cover-glass of the investi- 

 gator, and thus appear like degenerating nuclei in it. 

 The vesicles, which often appear in the cuticle, are prob- 

 ably artefacts due to the influence of reagents on the soft 

 cuticula of a dying ov a compressed animal. The cuticula 

 also macerates very rapidly, in fact it is often the first 

 part of the body to show death-changes, and may easily 

 become vesicular by the passage of fluids or gases into it 

 from the parenchyma or from the outside. 



In my own opinion this theory of the metamorphosed 

 epithelium breaks down, at least as a universal theory, 

 for several reasons. In the first place, the outer epi- 

 thelium is undoubtedly moulted in very many larval 

 trematodes, as has been observed by many competent 

 observers, and a worm can not both shed its epithelium 

 and still enjoy the possession of it, even in a modified 

 to rui. The theory can not thus have general application. 

 In the second place, even if the ectoderm of the embryo or 

 larva is cuticularized in certain cases, as has been ob- 

 served, the cuticula of the adult worm is not yet accounted 

 for, as the worm increases in size many-fold, often many 

 thousand-fold, while growing from the larval to the adult 

 condition. In other words, the cuticula of the mature 

 worm may be quite a different structure from that of the 

 larva, and if it is true that the cuticula of the larva is a 

 metamorphosed epithelium, then that of the adult is 

 formed of a different material and in a different way. In- 

 asmuch as the cuticula is constantly growing on its inner 



