AND THE CLASSIFICATION OF WORMS. 3 



my opinion for the following reasons : first, because I find that the supposed cuticula bends 

 in at the mouth (c/. fig. 10), and continues down the digestive tube into the two branches 

 of the same, where it becomes the basement membrane of the epithelial lining of the gut — 

 the "cuticula" is therefore the continuation of an undoubted basement membrane; secondly, 

 because our membrane corresponds exactly in appearance and position with that which is 

 really a basement membrane in Cestods, 1 but which had always been called " cuticula "; 

 it overlies a layer of glandular cells and muscles, 2 as in Caryophyllseus, Taenia and Amphi- 

 lina, 3 termed by German investigators, the Hautschicht, and wrongly regarded as the 

 epidermis, as I have elsewhere shown, — simply because the limiting membrane was neces- 

 sarily the cuticula, and the underlying cells consequently are epidermis. In Distomum 

 crassicolle and in other Trematods, there are muscular fibres close to the " cuticula," sepa- 

 rating it from the underlying cells, which quite agrees with the interpretation of it as a 

 basement membrane. If the view here advocated is true, we must account in some manner 

 for there being no epithelium discoverable outside our membrane. This may be done in 

 two ways : 1, the cells may have been destroyed in preparing the objects in the preserving 

 and hardening fluids ; or, 2, it may be a regular phenomenon of the development of 

 Trematods that the epidermis is thrown off. On the whole, I incline to the latter view, 

 because it would explain why no epidermis has ever been noticed upon any of the thousands 

 of living or freshly killed specimens that have been carefully observed by helminthologists. 

 There are, too, many cases known in which the larva? of Distoma are provided with a 

 ciliated external layer of cells, which is thrown off, or shrivels up, as development pro- 

 ceeds ; I may refer to Wagener, Pagenstecher, Leuckart, v. Linstow, Zeller, and many 

 others, as having observed this phenomenon. This justifies the supposition that the same 

 thing may occur in adult forms. If this should turn out to be the case, the difficulties 

 which now prevent any comparison of the epidermis of Trematods with that of the 

 remaining Plathelminths, would be entirely removed. Until further investigations shall 

 have determined this point, the question of the homology of the limiting layers of the 

 body of Distomum, etc., must remain an open one. 



The muscular system is not highly developed. There is but one distinct layer, formed 

 by a single row of longitudinal fibres (fig. 9, L) exactly as I have found in Caryophyllcms 

 mutabilis and Taenia sjj. ? from the intestine of a mocassin snake, Cenchris jjiscivortr*. 

 which had lived some time in Berlin and Wiirzburg. Leuckart 4 says that the Trematods 

 have three layers of muscles, the external being a circular coat ; but in B. hepalicum there 

 is also a single row of longitudinal fibres immediately under the so-called cuticula. In our 

 species there are a very few circular muscles (fig. 9, B) within the longitudinal layer. 

 The dorso-ventral, or the sagittal muscles, are quite numerous, and form the most conspic- 

 uous part of the muscular system. They run for the most part nearly straight up and 

 down, more rarely quite obliquely, but they show a great reduction in their number and 

 complexity of arrangement, as compared with the non-parasitic Pharyngocoela, approach- 



1 Schiefferdecker was the first to describe the true epider- 8 W. Salensky. Ueber Ampbilina. Zeitchr. Wiss. Zool., 

 mis of Cestods. Jena. Zeitscbr. Nat. Wiss. Bd. VHI, p. 459. xxiv. (1874.) p. 300. 



2 Cf. Schneider. Untersuchungen iiber Platthelminthen 4 Leuckart. Tarasitcn i, p. 459. 

 p. 5, where he especially mentions this point. 



