DEVELOPMENT IN CROSS-FERTILIZED EGGS 409 



reported by Moenkhaus (10). I have not verified his results. 

 Figure 23 of his paper was earHer interpreted by me as indicat- 

 ing lagging in this hybrid. The figure, however, shows only 

 one pole of the spindle and there is nothing to indicate the posi- 

 tion of the equatorial plane, which fact I overlooked in my diag- 

 nosis. His other figures are free from the undivided masses of 

 chromatin which are characteristic of the irregular mitosis found 

 in some crosses. This behavior justifies its inclusion in the group 

 of normally reacting crosses. 



DISCUSSION 

 1. The significance of the early mitotic disturbance in hybrid eggs 



Teleost eggs clearly exhibit a factor which regulates the 

 activity of the sperm chromatin in cleavage. The nature of the 

 mitotic disturbances which have been described above would 

 indicate that the immediate factor was a physical condition of 

 the egg cytoplasm, probably the normal state of fluidity or vis- 

 cosity characteristic of the division phase. The possibility that 

 physical factors of the sperm take part in this reaction should 

 not be excluded, but in the progress of cleavage the egg cyto- 

 plasm plays a more active role, while the elements contributed 

 by the sperm are relatively passive (15). In this sense the egg 

 determines the cleavage phenomena, the process of chromosome 

 separation as well as the rate of the antecedent processes. 



The results of heterogeneric hybridization in echinoderms are 

 analogous to those in fishes. We have several accounts of the 

 cytological events following cross-fertilization in these forms, 

 and in all of them, with one or two exceptions, the description 

 of the behavior of the chromatin resembles very closely that 

 given for fishes (1, 4, 5, 7, 8, 16). 



In order to be convinced that the phenomena are similar in 

 both forms, the reader has only to compare the figures given 

 here for the two Fundulus crosses in which the sperm of Cteno- 

 labrus and Prionotus was used and the figures already published 

 by the writer of the mitotic process in eggs of Stenotomus and 



