EMBRYOLOGY OF THALASSEMA MELLITA 



201 



in Ajiiphitrite the migration is not so extensive as it is in TJialas- 

 senia and Podarke. The gap does not close in Tkalassema un- 

 til about the thirteenth hour. 



The cells, that have thus migrated, increase rapidly in num- 

 ber and in the trochopore constitute a considerable area in the 



b p 



mid-dorsal region immediately below the prototroch (Text- Fig. 

 5). As most of the cells are small and thin and have dark 

 staining nuclei (Text-Fig. 6), their fate may be followed to a 

 late stage. In Podarke the migration of cells from the prae- 



