2(84: DR. J. B. GATENBT ON THE GEKM-CELLS AND 



mesogleal tissue. That the sperm is the instigator of this unusual behaviour 

 seems certain, and apparently any collar-cell may transform into a sperm- 

 carrying cell. From examination of Dr. E. S. Goodrich's small series of 

 Sycon ciliatum slides, I believe that in this form also the collar-cell acts as a 

 sperm-carrier, and Jorgensen's account of similar stages in Sycandra raphanus, 

 all misinterpreted, lead me to consider that the process described by me for 

 Grantia compressa will apply to other forms of sponges. 



It is evident, as Professor Dendy has himself pointed out to me, that two 

 distinct processes have been confused. The young oocyte is feci by a process 

 of phagocytosis. It is definitely established by Professor Dendy that certain 

 large amoeboid elements of the mesoglea carry other cell-elements to the 

 young sponge-oocyte, and the latter engulfs the food-matter so offered. The 

 cell-elements which bring such cell-food to the growing oocyte are unlike 

 the cell which later brings the spermatozoon to the oocyte ; moreover, this 

 process of feeding only takes place in small oocytes. After the latter have 

 grown to half their ultimate size, ingestion of other cells is rarely found to 

 occur, and, moreover, ingestion of other cells by the growing oocyte takes 

 place on any part of its surface, whereas the process of fertilization occurs 

 on one definite side of the oocyte. There can be little doubt that not only is 

 the process of phagocytosis in the oocyte different from the stages leading 

 to fertilization, but also that the cells engaged in the two processes are not so 

 alike as to lead one to believe that they are derived from the same source. 

 The cells engaged in bringing food-matter to the young oocyte are nearly 

 always much bigger than those which bring the sperm to the egg, and the 

 cell- contents of the two cells are not alike. 



(d) The Sperm-carrying Cell considered as a Mesogleal jimcebocyte? 



The sperm-carrying cell has been assumed by me to be a modified choano- 

 cyte or collar-cell. There may be critics of this view who would prefer to 

 take the other alternative, and look upon this peculiar cell as an amoebocyte 

 from the mesoglea : according to such critics, the amoebocyte would be much 

 more likely to behave in the manner of the sperm-carrying cells ; moreover, 

 it is true that some of the latter have nuclei rather unlike those of the collar- 

 cells, and similar to the true mesogleal amcebocytes. 



In the first place, one never finds amcebocytes near unfertilized but ripe 

 oocytes in the position in which the sperm-carrying cell later appears (text- 

 figs. 3 and 4). Secondly, I have never found spermatozoa in amoebocyte 

 elements of the mesoglea, and I have found several cases where sperms lie 

 within what I presume to be choanocytes (text-fig. 2, SP). Thirdly, there 

 is the fact that the position of the sperm-carrying cell is remarkably constant 

 (text-fig. 4) : now, if mesogleal amcebocytes carry the sperm to the egg, why 

 is this position so constant? Presuming that sperms swim through into the 



