CLEAVAGE PLANE AM) ENTRANCE POINT OF SPERM. 247 



sperm. In general, eggs that have stood in sea water for some 

 time after leaving the female, show a low per cent, of cleavages 

 through the entrance-point. Five hours after leaving the female 

 eggs fail to develop on insemination. 



These results seem to indicate that the first cleavage tend- to 

 pa-s through the sperm entrance point i. e., through the point at 

 the end of the indicator if the e--- lie fresh, undisturbed ami 

 fertilized with a single sperm. Why then do some first cleavages 

 fail to pass through this point? During this time a number of 

 experiments made by day and often at ni^hi immediately alter 

 the rapture- of the animals sho\\ed e eniialK the same propor- 

 tion-. 



Ringed Slide 



It was stated above, it will be remembered, that the egg tends 

 to lie with either pole uppermost. It. however, the eggs are 

 not disturbed those that settle on the side uill so remain. The 

 - are accessible to sperm at any point it not under pre tire 

 it no time in this study they were, Hie first cleavage always 

 rnt^ through the animal pole near the polar bodie-. <b\ioii-ly 

 then, the question of the relation of tin- hr-t cleavage plane to 

 the entrance-spot of the sperm cannot be -ettled by the 1 a\ 

 o! iho-e eggs in which the spermato/oa enter either at the point 

 In-low which the polar bodies are extruded or at a -p-i i 

 lr< mi ihi- point. 



In the next trial with very few eggs on ringed -.li.lt-, tho-e e-gs 

 in \\hirh the sperm indicator pointed either to the polar bodies 

 or to a point 180 from the polar bodir- \\ere not counted. This 

 trial re-ulied as follows: 



FIRST ( ii \\ AI.M I'l A 



Number. Entrance I'mm. MI. 



1 U 4 



2 4 



3 20 9 



()(her experiment-- with ringed -lide- -ho\\.d ab-uit the same 



proportions. 



l-'or fear that the rin-ed -lides were toxic owing to the vaseline 

 n-ed the\ \\ere abamloned and slides with cover >lips >up|)Oried 



