346 T^^ Philippine Journal of Science i9i3 



layer and the outer wall that, under any but the highest magni- 

 fications, the ectoderm seems to be lacking and the whole looks 

 to be a single, slightly thickened layer of mesogloea. The ecto- 

 derm cells of the hypostome are large and distinct, the shape 

 of the cells depending on the amount of contraction of the 

 hypostome when fixed. Those of the distal end are enlarged, and 

 contain large nematocysts which form a zone just below the 

 aperture (Plate II, fig. 3). This zone of nematocysts on the 

 hypostome was noted by Congdon ('06) in E. hargitti Congdon, 

 and it was considered by him to be a case of usurpation by the 

 hypostome of the protective function of the tentacles, as the 

 tentacles of E. hargitti have very few if any nematocysts. This 

 hypothesis does not seem to apply in the case of E. griffini, 

 however, as the tentacles are very heavily armed with nema- 

 tocysts. The ectoderm of the upper portion of the sense ring 

 is very striking. It consists of very large, elongated cells, 

 thicker than broad, with roughened outer ends (Plate II, fig. 

 5). The first 3 layers above the groove seem to be glandular, 

 having a granular deposit in their distal portions. These cells 

 in the male hydranth average between 25 and 30 /xfi in thickness, 

 but they are much thicker in the shortened female hydranth. 

 This region of thickened ectoderm of the sense ring is furnished 

 with a number of large oval nematocysts. 



The threads of these nematocysts are long and, when extended, 

 stain deeply in hsematoxylin, often making a very noticeable 

 fringe just above the sense groove (Plate I, fig. 1). Doctor 

 Griffin, who collected this hydroid, tells me that these nema- 

 tocysts are discharged with sufficient force to pierce the skin of 

 the back of the hand or the arm, inflicting a severe sting. 



The typical endoderm of the hydranth consists of very large, 

 lightly staining cells much thicker than broad. The free ends 

 of some of these cells seem to have amoeboid properties, sending 

 out pseudopodia into the gastric cavity. The cell walls are 

 distinct, and the nuclei are situated near the cell wall at the 

 distal end of the cell and only occasionally show nucleoli. While 

 remarkably clear and lightly staining, these cells are not vacuo- 

 lated. Scattered among these cells, however, in the upper walls 

 of the gastric cavity are found a number of gland cells with 

 vacuolated protoplasm and granular content (Plate II, fig. 1). 

 The average cells measure 75 by 45 by 25 jx/jl. Each cell con- 

 tains at its inner end from 3 to 10 or more zooxanthellse. 



The endoderm cells of the gastric cavity, which average about 

 75 fifj. in thickness, become much elongated on the upper surface 

 of the gastric cavity surrounding the opening from the hypostome 



