MATURATION OF THE EGG, AND PROCESS OF FERTILISATION. 43 



of its nuclear substance, which was described as a small, deeply 

 stainable spherule, there arises a vesicular nucleus (fig. 25 sk), which 

 acquires the same size and condition as the egg-nucleus. 



Fig. 22. Fig. 23. 



Fig. 22.- An egg of Ascaris megalooephala just fertilissd, after VAN BENEDEN. 



si-, Spermatic body, with nucleus, which has entered the egg ; /, fat-like substance of th& 



spermatic body ; kb, germiiiative vesicle. 

 Fig. 23. A stage of a fertilised egg of Ascaris megalocephala, somewhat plder than that of 



fig. 22, after VAN BENEDEN. 

 s'f, Spermatic body, which has penetrated deeper into the cortex of the yolk ; sp, polar spindle 



which has arisen from the germinative vesicle ; ch, chromosomes of the spindle. 



After the rapid and continuous accomplishment of these processes, 

 the egg of the Worm usually enters on a longer or shorter psriod of 



Fig. 24. 



Fig. 25. 



Fig. 24. -A still older stage of development, following that of fig. 23, of the egg of Ascaris 



megalocephala, after BOVERI. 

 tp, Polar spindle, which has ascended to the surface of the yolk ; ch, 2 x 4 chromosomes ; 



sic, spermatic nucleus, which ha? migrated into the middle of the egg. 

 Fig. 25 Egg of Ascaris megalocephala in preparation for the process of cleavage, after 



E. VAN BENEDEN. 

 ft, Two polar cells which have arisen from the polar spindle (*p) of fig. 24 by a repetition 



of the process of budding ; ei, egg-nucleus ; sk, spermatic nucleus already preparing to- 



divide ; ch, nuclear loops or chromosomes. 



rest. It now presents (compare fig. 25, which represents a stage 

 already further developed) at its surface within the vitelline mem- 

 brane two polar cells (pz), and in its interior two large vesicular 

 nuclei, the spermatic nucleus (sk) and the egg-nucleus (ei), the 



