404 J- SEILER. 



plates as Photos. 19-20, reproduced as accurately, as possible in 

 respect to the size-relations and relative positions, with an at- 

 tempt to identify the homologous chromosomes. The X-chro- 

 mosome happens, quite by accident, to be in all three cases in 

 the outer plate; quite as often it is found in the inner one. 

 The embryos have either 61 or 62 chromosomes. 

 January, 1917. 



EXPLANATION OF PLATE. 



None of the photographs retouched. Enlargement 2,000, excepting Fig. 10, 

 which is 1,000. 



