THE FERTILIZATION-PROCESS 



Within three minutes after the addition of a drop of 

 active spermatozoa to the eggs, remarkable changes take 

 place in each Q^g to which a spermatozoon has become 

 attached: a jelly flows out of the ectoplasm; the dull slightly 

 turbid ectoplasm in the unfertilized egg gives way to a 

 shining space crossed by strands. These changes can best 

 be observed under the microscope by adding spermatozoa 

 to eggs in sea-water which contains fine particles of Chinese 

 ink. The two photographs appended show living eggs 

 before and after insemination (Fig. 22). 





c d 



Fig. 23. — The fertilization-cone in the egg of Nereis (after Liliie). 



After the spermatozoon has become attached to the egg- 

 membrane, the egg beneath the site of attachment forms 

 a nipple-like projection, the cone, which shows itself well 

 developed twelve minutes after the mixing of eggs and 

 sperm, as can be noted in the Figs. I'^a and h. (Com- 

 pare these figures with those taken from the egg of Rhyn- 

 chelmis, Fig. 24.) Fig. 25 (from a drawing) pictures 

 a living egg in Chinese ink and sea-water fifteen minutes 

 after spermatozoa had been added to it. One marks easily 

 the germinal vesicle (too strongly drawn), the yolk spheres 

 and larger oil drops in the endoplasm, the ectoplasmic 

 strands, the entrance cone and the spermatozoon, plasma 

 membrane, vitelline membrane, the jelly and the surround- 



159 



