264 DR. J. B. GATENBY ON THE GERM-CELLS AND 



formation by extrusion of chromatin from the nucleolus into the cytoplasm." 

 Dendy's " chromidia " are the mitochondria ; so far as I can make out, Dendy 

 does not describe or figure true yolk, nor has any other author done so. 



Dendy shows that during oogenesis young oocytes engulf entire cells, 

 which are brought to them by special carrier (nurse) cells. This process is 

 very peculiar, and, so far as I can remember, unique in the Animal Kingdom. 

 Dendy also describes a remarkable process in which the nucleolus becomes 

 squeezed out to form lumps, which are extruded into the cytoplasm, and 

 from these lumps he considers the chromidia are formed. 



In his plate 24, figure 52, he gives a drawing of what we now know to be 

 the fertilization. Dendy tacitly accepted Jorgensen's interpretation of these 

 stages, but did not make a special study of development later than the full- 

 grown oocyte. 



Dendy's account of the origin of germ-cells from collar-cells has not met 

 with any sort of general acceptance, principally because English zoologists 

 have allowed themselves to be influenced by Weismann's germ-plasm theory 

 in an uncompromising form. More will be said of this matter later on. It 

 is merely necessary to add that the other view about the origin of the germ- 

 cells in sponges derives them from wandering amoeboid cells of the meso- 

 glea, and the wandering amoeboid cells are themselves derived during early 

 larval life from posterior granular cells or archseocytes (Minchin, 9). 



Both Jorgensen and Dendy describe a process whereby a part of one of 

 the pronuclei occasionally becomes separated, and lies in the cytoplasm as 

 an accessory separate nucleus, or " karyomere." Such a phenomenon does 

 not happen, according to my own observation, in healthy cells, and I consider 

 that the " karyomeres " are possibly accessory sperm-pronuclei, and that 

 such a cell as drawn by Dendy in his pi. 26, fig. 95, is a case of polyspermy. 



Subsequently to the writing of the above, I have seen many of Professor 

 Dendy's preparations showing young oocytes engulfing other cells (see (2) 

 pi. 24. figs. 50 & 51), and have found similar stages in my own slides. I 

 accept fully this part of Professor Dendy's account, and draw attention here 

 to the extraordinary character of this phenomenon. The oocyte of Grantia 

 is a veritable phagocyte, and markedly amoeboid and peripatetic. 



4. Material and Methods. 



The sponges used for this research were procured from the Plymouth 

 Biological Station during the months of July and August, 1919 ; the species 

 used was Grantia compressa, sometimes known as Sycon compression. Special 

 fixatives with directions for use were sent to Plymouth, and the specimens 

 were preserved there. I have to thank Dr. Allen, F.R.S., for seeing that 

 my directions were carried out. For some reason or other many of the 

 pieces of sponge showed signs of having died of asphyxiation, and, though 



