XV 



NEMATODA 



441 



ventral cell family, but before any further divisions take place certain 

 characteristic rearrangements of the members of the dorsal family 

 occur. On the right side a glides upwards and 6 downwards, whilst 

 on the left side a glides downwards and /? upwards (Fig. 343, D). 



At the next cleavage all four cells divide and the two daughters 

 of each are denominated 1 and 2, the more dorsal sister being indicated 



EMST 



ST 



FIG. 343. Early stages in the segmentation of the egg of Ascarix megalocephala. 

 (After Boveri.) 



A, 4 - cell stage in the T - condition seen from the right side. B, 4 - cell stage in the rhomb 

 condition seen from the right side. C, 6-cell stage seen from the right side. D, 8-cell stage seen 

 from the right side. 



by the suffix (1). As a result of the gliding that has taken place in 

 the previous stage, the four cells of the upper cell family on the right 

 side form a T-piece with a horizontal beam and a vertical cross-piece. 

 The beam consists of \ in front and & 2 behind, the cross-piece of a x 

 above and 2 below. The four cells on the left side form a rhomb c^ 

 and a 2 , lying rather in front of, but beneath, /^ and /3 2 . The four 

 cells of the ventral cell family form a horse-shoe with approximated 

 ends. Then a fresh rearrangement takes place, a : passes to the 



