76 P]RNEST WAREEN. 



At the base of the hydranth the perisarc terminates in a 

 well-defined groove (fig. G, ^3. g.), which is lined by a special 

 epithelium of grannlar cells. This groove is the remnant of 

 the chitin-secreting zone of ectoderm at the growing point. 

 It is from such a groove, or zone, that the perisarc is secreted 

 at the growing apices of stem, branches, or hydrorliiza. 



Fig. 7 is a vertical section through the growing apex of a 

 branch of the hydrorliiza, and the zone of ectoderm marked 

 jj. s. e. is seen to be densely granular, and it is here that the 

 perisarc is secreted. I do not believe that the ordinary 

 ectoderm below (o. e.) takes any part in the pi'oduction of the 

 perisarc {'p.). The apical portion of the growing branch is 

 naked {n. I.). 



E n d o d e r m . — The hy postome is lined by a regular columnar 

 epithelium, between the cells of which are wedged small, 

 vacuolated, and apparently glandular cells (fig. 6, v. c). 

 They stain deeply with ha?matoxylin, and consequently stand 

 out sharply from the surrounding columnar epithelium. 



Below the region of the hypostome the endoderm consists 

 of elongated, moi-e or less amoeboid cells, with vacuoles. 

 Between these, sometimes in clusters and sometimes solitary, 

 are inserted large, irregularly-shaped, glandular cells (fig. 6, 

 g. e. c), with large nuclei, and the cytoplasm is densely 

 crowded with large granules, which blacken with osmic acid. 

 These densely granular cells occur throughout the endoderm 

 of the genei'al coenosarc. 



At the base of the polyp the endoderm cells are taller and 

 constitute a more regular epithelium (fig. 6,6. c); towards 

 their base, inserted on the mesoglea, the cells contain very 

 large vacuoles. Often in this region the endoderm does not 

 consist of a single layer of cells. A sheet of smaller, more 

 rounded cells, with denser protoplasm, may cover a consider- 

 able area of the tall columnar epithelium at the base of the 

 polyp (fig. 6, r. e. c). 



The endoderm of the filiform tentacles is of the usual 

 septate character. In the capitate tentacles the endoderm 

 scarcely enters the "head." 



