vm. D. 5 



Light: Morphology of Eudendriu'm 



349 



cells by the egg cell is an admitted fact, if any zooxanthellae were 

 found in the hydroid described, they would be taken in with the 

 included cells. Furthermore, since inclusion in the egg cell has 

 been shown to be an important means of transmission of these 

 algae from generation to generation of hydroids (Mangan, '09), 

 we would expect to find them in the egg cells of any hydroid which 

 contains zooxanthellae. Allen's ('00) figures of Titbularia {Pary- 

 pha) crocea show several "included nuclei" which look suspi- 

 ciously like zooxanthellae, one of them (fig. 1, a, p. 305) even 

 showing a pyrenoid with the surrounding clear area. Whether 

 the spherical bodies in the eggs of E. ramosum and E. hargitti, 

 in Pennaria, in Tnbularia, and other hydroids be the nuclei of 

 included endoderm cells, as described by Congdon, Allen, and 

 others, or bodies which develop after the breaking down of the 

 included nuclei as held by Ciamician and Brauer, or zooxanthellae 

 as I believe, must be left for future workers to decide, but the 

 fact remains that sections of the ova of E. grifflni show no in- 

 cluded nuclei or pseudo-cells 

 and do show many unmistak- 

 able zooxanthellae which re- 

 semble in form and position 

 the pseudo-cells and included 

 endoderm nuclei described 

 and figured by the above- 

 mentioned authors. 



The ectoderm of the male 

 gonophore is about twice as thick as the normal ectoderm of the 

 hydranth wall. It is composed of narrower cells more closely 

 packed together, with more definite outer walls and more gran- 

 ular contents. A few small nematocysts are found in the 

 ectoderm, and several large nematocysts are usually found either 

 in the ectoderm of the base of the gonophore or in the ectoderm 

 of the hydranth immediately above or below the base of the gono- 

 phore. The endoderm which constitutes the spadix consists, 

 in the stalk of the gonophore, of a single layer of cells much 

 like those of the female gonophore, being granular and deeply 

 staining. In the region of the sperm chambers they are large 

 irregular-shaped cells with their long axes parallel to the long 

 axis of the gonophore. The sperm cells themselves are closely 

 crowded in the chamber between the ectoderm and endoderm, 

 making a characteristic labyrinthian figure (Plate II, fig. 6). 



Nematocysts. — The nematocysts of E. griffini are of two very 

 distinct types — large oval nematocysts found in a zone just above 



120986 2 



Fig. 5. Outline of a large nematocyst and 

 thread from Eudendrium griffini. 



