MUSEUM OF COMPARATIVE 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 protoplasmie zone of the mus- 
cular layer. 
The foregoing description of the muscularis differs essentially from 
that given by Bürger (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. XXXVIII. Fig. 5), whereas others of his sections 
(Figs. 9, 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 csophageal tube. 
Here as elsewhere this layer is highly refractive, and has walls 2 u 
thick, enclosing a lumen only 3 u in diameter. The deep layer, which 
surrounds the beginning of the wsophageal 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; atleast there are no transverse cell 
boundaries, though throughout its length one finds many nuclei which 
lie closely paeked together. In transverse sections the nuclear matter 
