EGG OF ALLOLOBOPHORA FOETIDA. 47 



In studying the .centrosomes of the fertilized egg, we are 

 brought face to face with the problem of the relative values 

 of the so-called egg and sperm centrosomes (Fig. 3). Some 

 investigators have asserted that in certain animal forms there 

 is no egg centrosome, and it has been suggested that in the 

 cases where it is unquestionably present it is merely a phylo- 

 genetic reminiscence, an out-of-date structure. (Allolobophora 

 foetida must be an extremely old-fashioned worm, for both its 

 maturation spindles possess this relic of the past.) (Figs. 2, 3, 

 4.) Other investigators find the centrosome present during 

 the constricting off of the polar bodies; but after the second 

 polar body is formed the attraction sphere totally disappears and 

 does not reappear in any form ; the sperm attraction sphere, 

 on the contrary, grows, becomes more and more pronounced, 

 divides, and forms two daughter attraction spheres, which con- 



FIG. i. Spermatozoon, showing spine, head, middle-piece, and tail. 



tinue to move away from one another until each occupies a 

 pole of the first cleavage spindle. This, you see, involves the 

 important assertion that the sperm centrosome is the ancestor 

 of all the centrosomes of the individual; for after each division 

 the mother centrosome is said by many investigators to divide 

 and to form the daughter centrosomes for the next division. 



These observations regarding the important role played by the 

 sperm attraction sphere involve most to those who hold certain 

 definite views regarding the male centrosome. They hold that 

 the male centrosome is furnished by the spermatozoon itself; 

 that it is the middle-piece of the spermatozoon before the 

 spermatozoon enters the egg (Fig. i); that after entering the 

 egg, the middle-piece contributes the substance which becomes 

 the centrosome of the so-called sperm attraction sphere (Fig. 3). 

 Thus, you see, according to some observers, the middle-piece 

 of the spermatozoon furnishes the substance which forms all 

 the centrosomes of the individual. They do not allow that the 

 egg even makes a contribution. 



