288 DR. j. B. GATENBT ON THE GERM-CELLS AND 



(h) Final Remarks. 



Professor Dendy has given me permission to state that he accepts my 

 explanation that what he described in his plate 24. fig. 52, as feeding of the 

 oocyte by nurse-cells, is really a stage in fertilization. 



The question of the true nature of the sperm-carrying cell is less well 

 established, but Professor Dendy considers that in all probability my 

 interpretation will be found to be the correct one. 



The problem of the spermatogenesis is a moot point, but I believe that 

 few will doubt that what I have described in text-fig. 1 and PI. 19. figs. 5 and 

 5 A are the true stages in Grantia. Haeckel, Polejaeff, and Dendy have 

 failed to bring forward convincing evidence as to the spermatogenesis, and 

 no cytologist acquainted with these questions would identify the "sperm- 

 balls " of these workers as authentic stages in the formation of spermatozoa 

 in any animal. 



Attention is drawn to the remarkable facts which other authors and I 

 have established with reference to sponge gametogenesis :— 



1. The young oocyte bodily engulfs large cells and feeds at their expiense. 



2. The oocyte and ovum are both amoeboid and capable of moving 

 through the mesoolea. 



3. Spermatozoa are developed in special nurse-chambers, possibly formed 

 of mesogleal cells. 



4. The spermatozoa are carried to the oocytes by special carrier-cells, 

 which are very probably collar-cells. 



5. The larva is nourished by a special nutrient chamber formed of 

 mesogleal cells. 



6. The pupal stages comprise many peculiar events, which lead to the 

 formation of the sponge. 



Probably in no other order does the gametogenesis and early development 

 present so many extraordinary peculiarities. 



This paper merely touches on a few of these peculiarities, and I hope in 

 subsequent work further to pursue the subject. 



28. Summary. 

 Choanocyte or Collar-Cell. 



1. The nuclear background contains a fairly dense basophil substance, 

 which is either a dense linin, network or a chromophil karyoplasm — more 

 probably the latter (PI. 19. fig. 1). 



2. The collar of the choanocyte has two thickenings, an inner and an 

 outer; the latter one is very well marked ; botli thickenings are more easily 

 seen in the partly withdrawn collar (PI. 19. fig. 1, B). 



3. The collar consists of delicate protoplasm which is best preserved by 



