I 



waite: antennal glands in homarus americanus. 185 



2. Histology. 



The histological character of the endsac differs distinctly from that of 

 the ectodermic sac, and the dividing mes-ectal line is sharply marked 

 (Plate 6, Fig. 51, In. mes-ec). The valve-like flap {vlv.) in the orifice 

 between the two sacs lies on the dorsal side, and its cells are connected 

 directly with those of the wall of the endsac, and are of the same na- 

 ture. In the region where the walls of the two sacs are adjacent, 

 they are not applied to each other continuously, but are separated by 

 spaces (Figure 51, lac. sng.) which constitute blood lacunae. This is 

 proved by the frequent presence in them of blood corpuscles (Figure 

 59), the structure of which is characteristic. These blood spaces are 

 separated at intervals by partitions or pillars (Figures 49, 51) connect- 

 ing the basement membranes of the two sacs. In structure these par- 

 titions resemble closely the tissue of the endsac. I have not traced the 

 continuity of these blood spaces with the general circulatory system. 

 They are not lined by an endothelial layer, as far as I am able to 

 discover. 



The cells of the endsac are all of the same general type, but show 

 two different forms, one (Fig. 52, Plate 6) being more flattened than the 

 other (Fig. 53, Plate 6). The more flattened cells occur in those regions 

 of the wall which are not adjacent to the wall of the ectodermic sac 

 (Fig. 51). All of the cells of the endsac have large nuclei, which lie close 

 against the free wall of the cell and in most cases cause a protrusion of 

 the cell into the lumen (Figs. 51, 53). The nuclei in the flattened cells 

 are more elongated in a direction parallel to the surface of the wall than 

 is the case in the more rotund cells of the other region (cf. Fig. 52 with 

 Fig. 53). Both kinds show a chromatic network. By the methods used 

 it was impossible to demonstrate any definite lateral cell boundaries, but 

 the extent of the cell territories is indicated by the position of the nuclei 

 and by the contour of the free face of the cells. The cytoplasm is finely 

 granular, and in most cases distinctly striated, the rows of granules be- 

 ing perpendicular to the surfacs of the wall of the sac (Fig. 53). This 

 granular striation would seem to indicate a secretory activity. There 

 is, however, no bounding striate cuticula on the inner face of the cells. 

 The wall of the sac presents a basement membrane, which is however 

 much less marked than that of the wall of the ectodermic sac, and 

 appears as a single line even under the amplification of a y^^ oil immer- 

 sion (Zeiss) and ocular 4. 



The cells of the ectodermic sac are very different in character from 



