No. I.] SPHYRANURA OSLERL 1 7 



appearance. The nucleus occupies the greater part of the cell- 

 body, the whole staining vividly, the nucleus somewhat more so 

 than the rest. The fibrils, however, lose the capacity for stain- 

 ing at a short distance from the central body, and on this 

 account the study of these structures is less easy. 



Longitudinal sections are the most favorable for a study of 

 the relations of the subcuticular cells to the muscular layers. 

 In this case the subcuticular cells give origin to fibres which 

 usually run in an oblique direction, and enter the longitudinal 

 muscle layer. Immediately under a tactile papilla several of 

 the fibrils may run, slightly curved, upwards through the 

 longitudinal muscular fibres to the circular layer, and, curving 

 again, are continued as circular fibres. It is to be noted that 

 sections of all the circular fibres under the tactile papilla 

 always appear thicker than elsewhere, owing to the fibres being 

 here directed obliquely, and consequently cut obliquely; and 

 this, coupled with the fact that the point of origin of such circu- 

 lar fibres as we determined was beneath a tactile papilla, has 

 led us to believe that all or nearly all of the fibres of the outer 

 muscular layer originate in this position. 



The structure of the muscular fibre could not well be deter- 

 mined during life. In specimens killed by chloroform the 

 fibre is seen to be made up of two parts, — a membrane and a 

 medulla. (Fig. 9, <3;.) The membrane is hyaline in appearance, 

 and distinct from its contents, which are finely granular and 

 apparently fluid. This condition cannot be demonstrated dis- 

 tinctly in fibres not relaxed by reagents. On the other hand, 

 one finds this to be the case in hardened preparations, although 

 the granules are much less numerous. 



A fine branching of the fibres at their terminations, such as 

 Salensky found in the parenchyma muscles of Amphilina, was 

 detected in the upper lip only of Sphyranura. (Fig. 6.) 



Only one observer, Poirier, describes the contracted condition 

 of muscle fibre in Trematodes. According to him the fibre, 

 when contracted, is swollen at regular intervals along its course ; 

 that is, alternate lengths of the fibre are thickened and con- 

 tracted. Our observations are opposed to this, the contraction 

 appearing rather as due to the fibre being thrown into a 

 wrinkled or zigzag course. Sometimes it seemed as if the fibre 

 assumed a spiral course; but of this we cannot be certain. The 



