Plate 1 



Above Young Echinus larvae, after BOVERI (1903 a). 



A. Larva reared from nucleated egg-fragment in which the egg nucleus 

 united with a sperm nucleus. B. Larva reared from non-nucleated egg- 

 fragment, from the same parents ; the nuclei in B are thus derived 

 from the sperm nucleus only, and are half as large and twice as 

 numerous as in A. 



Belo~M Stages of Amitotic division in nuclei of the Malpighian tubules of the 

 Stick-Insect Diapheromera, from MARSHALL. 



