THE BIOLOGY OF THE CELL SURFACE 



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consumed only about five seconds. And yet every egg 

 laid showed an attached spermatozoon and only one. 

 These observations were made soon after capture of the 

 worms: even so, the delicate males are apt to suffer some- 

 what in handling. In nature, therefore, this period is 

 presumably not longer than five seconds and may very 

 well be shorter. 



Only a very brief fraction of this period of five seconds 

 can be concerned with insemination per se. Most of the 

 time is consumed by the act of copulation, by the movement 

 of the spermatozoa to reach the eggs, and by the wave- 

 like muscular contraction of the female by which the eggs 

 are laid. That the fertilizable condition is here of extremely 

 short duration is further proved by the fact that eggs can 

 not be removed from the virgin female to a volume of sea- 

 water greater than that of the mass of eggs and the sea-water 

 in turn removed quickly enough to insure fertilization. In 

 other words, since it can be shown that sea-water does not 

 impair the fertilization-capacity of the spermatozoa, it 

 must impair very quickly that of the eggs. But the instant 

 that the spermatozoon becomes affixed to the egg, the sea- 

 water is harmless.^ 



The cytoplasm of eggs, then, at one or another stage of 

 maturation becomes suddenly fertilizable and remains so 

 for a longer or shorter period of time. Eggs die unless 

 fertilized, without exhibiting any change in nuclear state. 

 With fertilization, they pass beyond the fertilizable condi- 

 I , tion. I know of only one report,^ based on insufficient 



.^yj^ evidence, which claims that fertilized eggs can be re-fer- 

 tilized. In my experience, eggs having been fertilized lose 

 capacity for fertilization for neither they nor their frag- 

 ments can be fertilized again. ^ 



' Just, 191 Sh, 1915c. 

 ' Morgan, /S95. 

 •■' Just, /92ja. 



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