MUSEUM OF COMPAEATIVE ZOOLOGY. 151 



to these there is, however, the remnant of a deeper layer. Certain 

 cells (*, Fig. 59) project into the body cavity ; they are homogeneous 

 and lightly stained, in opposition to the muscle cells which remain un- 

 stained, and they contain nuclei at the proximal end of the cell. In 

 the body cavity of this specimen were found, in addition to the eggs, 

 cells of a very similar appearance to these, and at points along the wall 

 of the body cavity flattened cells had arranged themselves in the form 

 of an epithelium. All these points naturally suggest that this layer is 

 concerned in the production or nourishment of the sexual cells, and that 

 the remnant of the layer is in process of forming itself into a secondary 

 epithelium. The evidence is however too incomplete to justify more 

 than a suggestion ; but it points strongly to the existence of more than 

 one kind of histological element in the protoplasmic zone of the mus- 

 cular layer. 



The foregoing description of the muscularis differs essentially from 

 that given by Burger ('91, p. 635). Especial attention must be called 

 to the fact that the relative thickness of protoplasmic and contractile 

 portions as he gives it, namely, 2 : 1, is true in only one of the sections 

 he figures (Taf. XXXVllI. Fig. 5), whereas others of his sections 

 (Figs. 3, 4) represent exactly the opposite extreme. 



2. Alimentary Canal. 

 a. (Esophagus. 



Attention has already been called to the fact that one finds a shal- 

 low dorsiventral groove (Fig. 2) at the front of the head, and that the 

 minute mouth opening is located at the centre of this groove (Plate V. 

 Fig. 63). The cuticula, which is extremely thick at this point, is 

 here infolded ; the deep layer extends but a short distance, while the 

 external layer is continued backward to form the oesophageal tube. 

 Here as elsewhere this layer is highly refractive, and has walls 2 fjt, 

 thick, enclosing a lumen only 3 /a in diameter. The deep layer, which 

 surrounds the beginning of the oesophageal tube, measures 9 /a in thick- 

 ness. After this layer stops, the chitinous oesophageal tube, which is 

 the continuation of the external layer, becomes somewhat thicker, and 

 it is seen that the entire tube is contained within a cell of small diam- 

 eter (Plate III. Fig. 32). From longitudinal sections it is seen that the 

 cell is coextensive with the tube ; at least there are no transverse cell 

 boundaries, though throughout its length one finds many nuclei which 

 lie closely packed togethei'. In transverse sections the nuclear matter 



