Observations anel Exper.ments on the Otenophoro Egg-. 



•event tins jelly layer gives .a splendid criterion for distinguishing at 

 .a glance fertilized egg from unfertilized. 



One other phenomenon accompanying fertilization is that the 

 •ooplasm suddenly acquires greater consistency. This is especially 

 frappant after the formation of an ectoplasmic thickening around 

 the spermatozoon. One can hardly fail to notice this change when 

 •experimenting upon various stages of the egg. 



The entrance of the spermatozoon can readily he seen in the 

 ■egg of Beroë. Fig 5 (PL I) shows a surface view soon after its 

 penetration into the egg. A réfringent hody (acrosome?) is seen a 

 little apart from the head. Behind the head is a dark body, 

 sperm-centre, provided with long rays. Soon, however, the rays 

 ■disappear. In a side view one sees an entrance-cone consisting of 

 a thickened external homogeneous layer and also considerable 

 .accumulated ectoplasm. The entoplasmic alveoles are arranged 

 radially (PI. I, Fig. 6). In them no rays are seen in the living 

 -egg. In section, however, distinct long rays come into view, 

 which extend from the straightened alveolar walls of the ectoplasm 

 into those of the entoplasm. As is seen in Figs. 7 and 8 (PI. I) 

 the ectoplasmic accumulations remain for some time, so that by 

 them one can tell at once how many spermatozoa have entered the 

 •egg. On one occasion I saw an egg with as many as five of them 

 in it. Polyspermy in this form is not at all a physiological 

 phenomenon. It usually takes place when eggs are kept too 

 -crowded in a jar. I know nothing about the fate of those sperm- 

 nuclei which fail to unite with the egg-nucleus. Yet judging from 

 the fact that in many cases polyspermy does not lead to 

 .abnormal cleavage ; those sohtary sperm-nuclei seem to degenerate 

 .■in situ. 



IV. Cell-division. 



a) The First Cleavage. 

 I could not make out how or where the germ- nuclei 



