290 THE ANATOMY OF CESTODES. 



life be clad with an epithelial layer the ectoderm. But general 

 statements of this kind must vary with the growth of our experience, 

 and it is only to the results of experience that we can attach 

 decisive importance. 



Yet another argument against the prevalent explanation of the 

 so-called subcuticula as an epithelial layer is found in the fact that 

 it is not directly adjacent to the cuticle, but is in fact separated from 

 it by a layer of fibres crossing at right angles. 



Our attention is first directed to the existence of this peripheral 

 fibrous layer by the appearance of a thin section of the skin, which 

 shows on its surface a delicate, extremely fine lattice- work. The lines, 

 which form this, run very regularly transversely and longitudinally, 

 and turn out on further examination to be the contours of fibres, 

 which are arranged one over the other in simple layers. The outer- 

 most are the transverse or circular fibres, which form a continuous 

 sheath, while the longitudinal fibres are separated by interspaces, 

 through which run the external processes of the spindle-shaped cells. 



This difference between the two layers of fibres is obviously the 

 reason why many investigators have claimed for each a distinctive 

 character. The longitudinal fibres have been very generally regarded 

 as muscles, but those running circularly have sometimes been regarded 

 as connective-tissue fibrils (Rindfleisch), and sometimes as integral 

 parts of the cuticle (Schiefferdecker and Steudener). Only a few 

 observers (Leuckart, Nitsche, Schneider) have regarded them as a 

 layer of circular muscle fibres. 



I still hold to the last opinion, because if the fibres of the two 

 layers be observed under the same conditions, they have the same 

 optical characters; and, besides, there are cases, as in the so-called 

 caudal bladder of the Cysticerci, where both circular and longitudinal 

 fibres are in their thickness and microscopic characters undeniably 

 muscular. They are indeed usually paler and narrower than most 

 muscle fibres, but these present so many striking differences that one 

 cannot lay much weight on such peculiarities. 



After this discussion of the facts of the case, I do not think that 

 I am wrong in claiming the subcuticular fibrous structure of the 

 Cestodes as a musculo-dermal layer. 1 The other muscles penetrating 

 the connective substance of the body might then be called the 

 parenchymal muscular system. 



1 Previous investigators have also sometimes spoken of a musculo-dermal layer in the 

 Cestodes, meaning thereby usually the muscles of the cortical sheath, including generally 

 the transverse fibres surrounding the middle layer. These I designated, not quite cor- 

 rectly, in the first edition of this work as the layer of circular fibres, and indeed as the 

 " deeper" or "inner" layer, as distinguished from the subcuticular system. 



