A. A. MERLIN ON THE SPERMATOZOON OF THE RAT. 191 



The nucleus and middle-piece are l)elieved to play the most 

 important part in fertilising the ovum, the latter being con- 

 sidered to be the fertilising element par excellence, since it is 

 supposed to contain or to be itself a metamorphosed centrosome, 

 which, when introduced into the e^^, stimulates division 

 (Wilson). The invariable truth of this latter point, however, 

 may be open to doubt, as in a photograph annexed to a paper 

 "On the Human Spermatozoon,"* read by Mr. Edward M. 

 Nelson before the Quekett Microscopical Club on November 21st, 

 1890, a tail, middle-piece, and cup are clearly shown, from which 

 the " head" or "spore " has fallen, while in another photograph 

 a " spore " is depicted without a cup. This observation appears to 

 be in opposition to the theory that in every case the head and 

 middle-piece of the spermatozoon together enter the ovum, the 

 tail alone being carried off by the formation of the vitelline 

 membrane, and that the sperm aster is always developed around 

 the material of the middle-piece. That the sperm aster is de- 

 veloped round this material in the case of the sea-urchin 

 Toxopneuates variegatus seems, however, to be proved by the 

 photographs published in Dr. Wilson's " Atlas of the Fertili- 

 sation and Karyokinesis of the Ovum" (1895). . 



The spermatozoon of the rat is thus described in Schafer's 

 "Essentials of Histology" (2nd edition, 1887): "The head is 

 long, and is recurved anteriorly; it is set obliquely on the 

 middle-piece, which is also of considerable extent, and has a 

 closely wound spiral filament encircling it in its whole length." 

 (H. II. Brown). 



Having spent a considerable time in the examination of an 

 exceedingly fine stained preparation of rat spermatozoa in my 

 possession, with objectives of the very highest class and optical 

 excellence, employed under such conditions as insure the most 

 critical results, I venture to claim that the head of this sper- 

 matozoon does show something strongly resembling an organised 



* Journal Q.M.C, Ser. II., Vol. IV., p. 264, and Plate- 18, Fig?. 2 

 and 3. 



