810 FOOT. (Vor. XII. 
ena differing in that the anterior end of the head of the sper- 
matozo6n produces a cone, whereas it is the middlepiece that 
produces the attraction sphere. 
Before the first polar body is formed we find a cone the 
moment any part of the head of the spermatozoon penetrates 
the egg, and the extent of the cone appears to depend upon the 
length of head which has entered: if a relatively short piece 
of the head has entered, we find a relatively small cone. The 
sperm attraction sphere, on the contrary, does not appear until 
the middlepiece is within the egg, and in other forms this fact 
has been cited as evidence for the assumption that the centro- 
some of the sperm attraction sphere is of the substance of 
which the middlepiece of the spermatozo6n was formed. 
The more important observations adduced to prove that the 
male centrosome is formed from the middlepiece are the fol- 
lowing: First, the attraction sphere does not appear until 
after the spermatozoon has entered the egg. Secondly, it 
appears at or near the point formerly occupied by the middle- 
piece of the spermatozoon. Thirdly, the middlepiece and the 
centrosome have been shown to select the same stains. Might 
not the first and second observations be cited with equal perti- 
nence to prove that the spermatozoén produces merely a physi- 
ological effect upon the cytoplasm? The third observation has 
a more definite bearing upon the point in question. In the egg 
of Allolobophora foetida, however, I have differentiated by two 
methods the middlepiece of the spermatozoén from the male 
centrosome. This differential staining might be explained by 
the assumption that the middlepiece undergoes a physiological 
change on entering the egg; but as the head gives no such 
evidence of physiological change, are we justified in assuming 
without further evidence that this takes place in the middle- 
piece? 
The centrosomes of the egg of Allolobophora foetida \end 
support to the view that the centrosome is a mechanical center 
— the expression, rather than the cause, of cell activity. The 
egg attraction sphere is present during the two maturation 
divisions, but after the second polar body is formed and the 
female pronucleus begins to develop, it totally disappears (Fig. 

