14 GEOKGE T. HARGITT 



3. OBSERVATIONS UPON SPERM CELLS 



Male gonophores are produced upon different colonies than the 

 female gonophores and differ from them in appearance and some- 

 what in structure. So far as my observations go, I can confirm 

 the conclusions of Weismann ('83) that the sperm cells of Euden- 

 drium arise in the stem or stalk of the hydroid from entoderm 

 cells and migrate into the gonophore. The growth of the 

 gonophore also aids by passively carrying these cells into position. 



A brief account of the formation of the gonophore is necessary 

 in order clearly to understand the significance of germ-cell for- 

 mation. The growing point of the hydroid is in the stem, imme- 

 diately below the terminal hydranths where the cells are richly 

 protoplasmic and the ectoderm and entoderm not differentiated 

 into gland cells, nettling cells, and the like. The narrow, grow- 

 ing zone is followed proximally by the usual coenosarcal tissue 

 with its differentiated cells of various sorts, both in ectoderm 

 and entoderm. Newly formed lateral hydranths and gonophores 

 develop at a point some distance proximal to this growing zone 

 and their origin may be recognized, before there is any actual 

 new growth, by the change in the character of the cells. This 

 recognizable change is the production of a new growing zone 

 in the coenosarc at that point, and this involves a regressive 

 change of the differentiated ectoderm and entoderm into the same 

 small, richly protoplasmic cells which are found in the growing 

 point of the main stem. After this change has occurred the 

 perisarc opposite this group of cells is dissolved, an evagination 

 of the coenosarc occurs and gradually a new structure is differ- 

 entiated from this bud. 



Thus in the production of gonophores as well as of hydranths, 

 differentiated cells undergo a regressive change and after fur- 

 ther growth once more becomes differentiated. There is no 

 difficulty in demonstrating this typical method of growth in fe- 

 male as well as in male colonies. This is very significant, when 

 it is also found that the male germ cells arise in the stem adja- 

 cent to the gonophore, apparently from regular entoderm cells. 

 If active, growing, undifferentiated cells may, by differentiation, 



