126 CHARLES V. MORRILL. 



EXPLANATION OF PLATE II. 



a-c, Archimerus allernatus. a, a stage letter than PI. I., d -the sperm head has 

 been transformed into the male pronucleus and is still advancing into the egg pre- 

 ceded by its aster and a small clear area, b, an early stage in the copulation of 

 the male and female pronuclei each is in contact with a clear area and an amphi- 

 aster lies between them, c, a later stage in the copulation of the pronuclei the 

 nuclear membranes are still intact; seven chromosomes appear in the lower nucleus, 

 the wz-chromosome being absent; a faint aster appears on the right, d, Protenor 

 belfragel: First cleavage prophase, polar view the male and female groups are 

 still separate, one of them being incomplete; an idiochromosome appears in each 

 group. The magnification is 1,375 diameters. 



