XV 



NEMATODA 



441 



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

 characteristic rearrangements of the members of the dorsal family 

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

 on the left side a glides downwards and (3 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 



B 



EMST 



ST 



FIG. 343. Early stages in the segmentation of the egg of Ascuri.<t 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. 1>, s-rell sl.-i-r 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 5 1 in front and &., behind, the cross-piece of a x 

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

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

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

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



