Life-history and Anatomy of the Appendiculate Distomes. 357 



cuticula and gave it the appearance of being subject to disintegrating 

 influences of some sort. I have rarely found these structures in 

 worms which were taken in the sea-water. Similar structures have 

 also been observed in the adult appendiculate Distome by Juel (1890, 

 p. 10) and by other authors in other worms. I have also seen the 

 cuticula in certain individuals thickly beset with fine radial lines 

 extending through it (PI. 26, Fig. 6 s.mem\ which have also been 

 seen, among others, by Leuckart (1886 b, p. 186) and Stiles (1894, 

 p. 232) in Fasciola hepatica and F. magna respectively, and called 

 palisade-like structures. These structures may appear in certain 

 portions only of the cuticula of a worm; I have noticed, in fact, that 

 worms which were contorted or bent when killed may show them in 

 those portions of the cuticula which were compressed by the contortion, 

 while the remainder of it will be quite free from them, and I think 

 that one explanation of them may be that they are the result of the 

 compression of the soft cuticular substance. Juel (1890, p. 10) found 

 in the cuticula of the adult worm in the inner portion of the inner 

 layer a layer of minute vesicles: in the cuticula of the appendix, also, 

 besides these, he found other, larger, and more irregularly placed vesicles. 



Similar vesicles and also concretionary structures of various kinds 

 have frequently been found in the integument of Trematodes by various 

 authors, of whom I will mention Ziegler (1883), Braun (1892, p. 590), 

 and MoNTiCELLi (1892 and 1893), and have often been intrepreted 

 by them to be the remains of degenerating nuclei. They conclude 

 from their presence that the Trematode - integument is a meta- 

 morphosed epithelium. Juel remarks that the larger vesicles he ob- 

 served in the cuticula of the appendix may be nuclear remains although 

 he is evidently not inclined to regard them as such: the layer of 

 smaller vesicles he declares cannot be nuclei. 



It seems to me that the presence or absence of such integument- 

 ary vesicles and concretions need not cause surprise, and that the 

 whole matter has been very satisfactorily explained by Looss (1894, 

 p. 116 — 119). They are, according to that author, pathological 

 structures which may make their appearance in the moribund or com- 

 pressed animal. In such an animal the soft and semi-fluid inner cuti- 

 cular layer may easily become vesicular by the passage of fluids and 

 perhaps gases into it from the parenchyma. The outer cuticular layer, 

 being harder and tougher, rarely assumes such a character; it may, 

 however, together with the inner layer, show large numbers of tine 

 radial lines, like the palisade-like structure above described, which 



