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388 FRANK R. LILLIE 
anterior part of the sperm into the egg to prove whether or not 
the sperm nucleus without the centrosome, which is contained 
in the middle piece of the spermatozoon, would cause the produc- 
tion of asters in the egg-cytoplasm. 
As Boveri, among others, has pointed out, there is not only 
one, but several stages of inhibition in the history of the egg. 
This may be illustrated by noting the stages at which in the eggs 
of various animals the need for fertilization arises. In some eggs 
it is before the rupture of the germinal vesicle (e.g., Nereis), 
in others at the time of the mesophase of the first maturation 
spindle (e.g., Chaetopterus and Cerebratulus), in others again 
after the formation of the first polar body (e.g., Amphioxus, 
amphibians), in others again, not until after the formation of 
both polar bodies (e.g., sea-urchin). There is no doubt that the 
last stage of inhibition is the most difficult one to overcome, both 
because many eggs pass by the earlier stages without apparent 
specific stimuli and also because it is possible to cause eggs that 
normally stop at the first or second stage of inhibition to pass on to 
the last stage by stimuli that are ineffective when this stage is 
reached, (e.g., Nereis as noted in this paper and Chaetopterus as 
noted in various earlier papers). 
The nature of the inhibition that causes the need for fertiliza- 
tion is a most fundamental problem. Is it the same in all these 
cases, 2.e., a gradually increasing inhibition that may be effect- 
ive before maturation, but in some cases not until maturation 
has progressed a certain distance, or even until it is complete?! 
If it is the same cause at all these stages then it is certain that the 
need for fertilization is not due to any defect of the egg-centro- 
somes, for the pause takes place in Chaetopterus (e.g.) while the 
egg-centrosomes are at the very height of their activity. If, 
‘Bataillon (10) holds the view that the nature of the inhibition is the 
same whether the arrest is at the stage of the resting nucleus or in the height of 
karyokinesis. He holds the view that the inhibition is due to accumulation of ex- 
cretory products and that the stimulus to development is essentially a process of 
elimination. Bataillon’s paper was received after my own was completely written. 
His interesting results will be considered more fully in my next paper. In Part 
I of the present paper (last paragraph) I have presented a view similar in some 
respects to Bataillon’s. 
