AMI'HIGONIC HERKDITY 



233 



van Beneden was the first to prove that the number of these 

 idants is the same in both of the conjugating-cells, and this dis- 



'■\.TU>9 



'Rkl 



KkT 



noo 



W 



Fig. 18. — Diagram of the fertilisation of the egg in Ascaris megalocephala. — 

 (Compounded from the figures and descriptions of Boveri and others.) 



I. — The sperm-cell (i/) is about to enter the ovum, which contains a nucleus {noz>') 



and centrosome {cs). Rk I and Rk 11 — the two primary polar-bodies, the first 

 of which has divided into two; each contains two idants. 



II. — The sperm-nucleus {nsp) has passed into the egg. near the nucleus of which 

 it is situated. Each of these nuclei contains two idants, and also a centrosome, 

 which has divided into two. 



III. — The two nuclei are now close together: the centrosomes, with their ' spheres 

 of attraction,' are connected together in pairs, and are situated at the poles of 

 the spindle, which is already visible. 



IV. — The nuclear membrane has disappeared, and the first embryonic nuclear 

 division is now taking place. 



coverv — which has since been confirmed in the case of a large 

 number of species of animals, and has been proved quite recently 



