FERTILIZATION OF NEREIS. 



199 



In some cases (Table II.) it was possible to note the time of 

 formation of the first polar body. The average of elapsed time 

 after insemination was 35.8 minutes and no correlation was 

 noted between the duration of attachment of the sperm and the 

 time of formation of the polar bodies. 



TABLE I. 



As noted in Table I. some eggs were fixed at about time of the 

 first cleavage with view to study of cytological changes. Too 

 few of these have survived the ordeal of embedding and sectioning 

 to make any detailed study valuable. I noted that in some cases 

 only chromosomal vesicles and in other cases well-formed chro- 

 mosomes were present at the time of the first cleavage spindle. 

 This may be compared with the observation of Lillie ('15) where 

 chromosomes were formed in eggs from which sperm were re- 

 moved by centrifuging but not in eggs which were caused to 

 maturate by centrifuging without insemination. 



The appended tables outline the experiments. Full data are 



1 Egg fixed at about time of expected first cleavage. No indication of cleavage 

 at that time. 



2 Poly-spermy observed in same lot on cover-slip. 



