EARLY DEVELOPMENT OF GRANTIA COMPRESSA. 279 



the oldest spermatids I could find, and in PI. 19, fig. 6 I have drawn the 

 sperm possibly just after it has entered the collar-cell. The tail of this sperm 

 has been added to my drawing. From what evidence I gained by examining 

 a number of ripe sperms lying in collar-cells, I believe that the only 

 change undergone by the sperm in this position is tbe loss of its tail or axial 

 filament. The nucleus of the sperm, after entry into the collar-cell, might 

 swell a little, but I have no evidence that such is the case *. It is only 

 when the sperm is drawn into the egg that the former breaks into parts, 

 and the nucleus begins to swell. The collar-cell has no such effect on the 

 sperm : this is a very interesting point. 



Gorich, however, in Spongilla draws the sperm quite differently from that 

 of Grantia, and if the free sperm of the latter resembles that of Spongilla it 

 is certain that some change comes over the Grantia sperm after entry into 

 the collar-cells. G-orich's account I do not trust in details. 



20. Changes hi the Collar-cell brought about by the Entry of the 

 Spermatozoon. 



While most sperm-carrying cells at the stages drawn in text-fig. 3 closely 

 resemble the collar-cell, it is true that by the time the former reach the 

 oocyte some undoubted changes have taken place, especially within the 

 nucleus. 



The example drawn by Professor Dendy (2) on PL 26. fig. 52 of his paper 

 is a fairly typical case, such as I have occasionally noted in my own 

 material ; a similar example is drawn on PI. 20. fig. 16 of this paper. 



I find that a good deal of variation in the general appearance of the nuclei 

 of the sperm-carrying cell can be noted, and some nuclei are exactly similar 

 in size, shape, and staining-power to the collar-cell nucleus, while others 

 lack especially that dense substratum peculiar to collar-cell nuclei. I consider 

 that this partial clearing-np of the dense nuclear substratum is caused by the 

 prolonged presence of the sperm, and is in some way connected with the 

 amoeboid phenomenon of the metamorphosed collar-cell. 



In addition to this occasional change, all sperm-bearing collar-cells lose 

 their collar and flagellum, and become amoeboid. As would be expected, 

 most sperm-bearing cells are a little larger than the unmodified collar-cell : 

 this is due to the presence in them of the sperm. 



21. The Fate of the Sperm-carrying Cell after the Sperm passes into 



the Oocyte. 

 The sperm-carrying cell lying upon the surface of the oocyte is a most 

 conspicuous object, yet in the cleavage-stages subject to fertilization this cell 

 could not any longer be made out. Having examined a number of early 



* I have lately procured evidence that the sponge sperm is filiform and flagellate, sa a 

 great change conies over it after entry into the collar-eel] (see Journ. Roy. Micr. Soc. L920). 



21* 



