THK RELATION OF THE FIRST CLEAVAGE PLANE 

 To I Hi; ENTRANCE POINT OF THE SPERM.* 



ERNEST E. JIM 



I hiring the summer of IQII at tin.- Marine Biological Labora- 

 tory under the direction of ProK r Frank R. Lillie, I was cii- 



''! in tlu- study of the eggs of AY/r/\ of certain cvtolo-ical 



problem- tin- results of which will appear later. The question 



ot the relation of the entrance-point of the ^perm and the tir-t 



plane occurred to me. A verv pretty method made 



-ible in .t satisfactory- fashion the determination of this relation 

 the result- ol which this paper embodies. I here take this oppor- 

 tunity to express my thanks and sense of gratitude to l'n>te ! 

 Lillie for hi- ins[>iring interest in the work of which this is a part. 



MATERIAL AND M i i in >i>-. 



Tin of Xereis when shed are irregular i n -h.ipe din- i<> 



I ire nre \\hile in the body of the female. They soon till oni in 

 the >ea \\ater, measuring about IOO /z eqnatoriallv and -oine\\ hat 

 less in a polar direction. There is, ln\\e\er. i dial of 



indi\ idnal ~i/e variation in the j i\ en female Tli 



are almo-i transparent, colored a pale ^reen liy numerous deuto- 

 plasin spherules distributed throughout the endoplasm; around 

 the eijuator i- .m irregular double -irdle of 14 to jj i.il drops 

 I ig i hi polar view the lar-e -erininal ve-icle appears to be 

 in die center of ih. h i-. lio\\ t -\cr. s|j-htl\- i-lnn^ated in 



the pol.ir diri-ciion. The pnlaritx' of the o\ is, therefore, 



expressed by tin- polar tlatteninu already mentioned, the position 

 of tin- oil dro|>. and the form of the nucleus. 



A- ha> been >ln'wn (^Lillie, 'in there are not two membranes 

 in the unfertili/ed egg of Nereis, but rather a single vitellinc 

 membrane external to the radially striated cortical layer ("zona 

 radiata," \\ilson) of the egg. The ov<>cvte remains thus with 



*A11 ilrawin.ys. oi living t-v;u~. made with the aid of a camera luci'la. 



