STUDIES OF FERTILIZATION IN NEREIS 
Ill. THE MORPHOLOGY OF THE NORMAL FERTILIZATION OF NEREIS 
IV. THE FERTILIZING POWER OF PORTIONS OF THE SPERMATOZOON 
FRANK R. LILLIE 
From the Marine Biological Laboratory, Wood’s Hole, Mass., and the Hull 
Zoological Laboratory, University of Chicago 
FORTY-EIGHT FIGURES 
ELEVEN PLATES 
In the preceding numbers of these studies dealing with the 
cortical changes of the egg, and with partial fertilization, refer- 
ence has been made to certain phases of the normal fertilization. 
A detailed study was found to be necessary to clear the way for 
further considerations. The results of this detailed study are 
presented in the first part of the present paper. The second part 
deals with the fertilizing power of portions of the spermatozo6n 
and with the theory of fertilization. 
Ill. THE MORPHOLOGY OF THE NORMAL FERTILIZATION OF NEREIS 
1. The spermatozoén: (Fig. 1, a, b, c, d) 
The spermatozoa are unusually large. The head terminates 
in a very delicate perforatorium which possesses a slight distal 
enlargement.! Between the base of the perforatorium and the 
chromatin of the head is some differentiated material forming a 
head-cap (h. c.). This is very distinctly differentiated in position 
and staining reaction from the chromatin of the head. The chro- 
matin of the head is not so condensed as in most spermatozoa; 
1 In the living spermatoén the perforatorium is shorter and shaped more like 
the spike of a helmet. 
413 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 12, No. 4 
MAY 1912 
