GENERATIOX, SEX. AND OXTOGEXY 



219 



uals, then, of course, it is like the others of the shghtly com- 

 plex animals in this respect. But as soon as we rise higher in 



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t. 



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Fig. 125. — Fertilization of Petromyzon fluvial His: A, Sperm nucleus in periphery of the 

 egg plasm; B, yperm nucleus in periphery of the egg plasm. an«l egg nucleus ap- 

 proaching; C-E, fusing of the ogg and .-iktiu nuclei, and appearance of the alters; 

 F, cleavage of nucleus. (After llcrfort.) 



the scale of animal life, as soon as we study the more comjlex 

 animals, we find that the egg cells and sperm cells arc almost 



