EFFECTS OF IXJURY UPON SPERM. 237 



tion with normal sperm. These features have been described 

 previously (Lillie, F. R., 'n, '12) but an outline of the cyto- 

 logical changes is necessary for a proper understanding of the 

 observations on the experimental material. My studies have 

 been based upon my control series and upon slides loaned to me 

 by Professor Lillie. The latter are especially fine and show 

 clearly all of the conditions which he has described in his papers. 

 Immediately after a spermatozoon becomes attached to the egg 

 by means of its delicate perforatorium the contents of the coarse 

 alveoli of the cortical layer of the egg begin to pass to the exterior 

 where, in the course of fifteen minutes, they form a thick layer 

 of jelly. A perivitelline space now occupies the position formerly 

 held by the cortical layer of the egg. An entrance cone forms 

 from the egg cytoplasm just beneath the spermatozoon and, about 

 three quarters of an hour after insemination, draws the sperm 

 head, in the form of a thread, into the egg, leaving the tail and 

 middle piece outside. This usually occurs during the late 

 anaphase of the first maturation spindle. The sperm head now 

 begins to grow larger and, retaining its connection with the 

 entrance cone, penetrates the egg protoplasm. The whole 

 complex, as it passes to the yolk free area of the egg, rotates so 

 as to bring the sperm nucleus ahead and nearer to the center 

 of the egg. Meanwhile the sperm aster appears at the pole of 

 the nucleus which is opposite the cone and soon divides, forming 

 an amphiaster. Following the formation of the second polar 

 body, the egg aster fades away and the egg chromosomes swell 

 and form conspicuous vesicles, each one with a distinct chromatic 

 nucleolus, which slowly fuse together to form the egg nucleus. 

 By this time the sperm nucleus has increased in size and presents 

 an appearance much like that of the egg nucleus, near which it 

 has come to lie. The two nuclei now fuse and the asters of the 

 first cleavage spindle, presumably derived from the sperm 

 amphiaster, are seen on opposite sides of the cleavage nucleus. 

 The process of cleavage then ensues. 



B. Experimental. 



In the experimental material it has proved difficult to establish 

 a definite seriation in the cytological observations, since, as 



