Ill DIFFERENTIATION 97 



amphikaryotic nuclei of normally fertilized ova. The irregu- 

 larity in the behaviour of the male chromatin sometimes 

 affects the female, and one or more of the cells may fail to 

 obtain a complete set, and this is put forward as the cause of 

 the irregular development of some of the larvae. 



The segmentation of these ova is of the usual Echinoid 

 type (in a certain percentage of cases) and swimming blastulae, 

 and later, plutei, are produced from them. The rate is 

 slow. 



Godlewski has found that when Echinoid eggs are fertilized 

 with the sperm of Chaetopterus or Dentalium the elimination 

 of what is presumably the male chromatin takes place after 

 the male and female pronuclei have fused, but before the 

 chromosomes and the spindle appear. 



In all these cases the larva is of the purely maternal type 

 in every respect ; it is a pluteus, and shows no trace of any of 

 the characters of the larva of the male parental form. The 

 earlier processes of cleavage and gastrulation are also those 

 characteristic of the ovum employed. The male chromosomes 

 may persist or be sooner or later eliminated. In no case do 

 they exert the slightest influence. 



Identical results have been obtained by Moenkhaus and 

 Loeb with the heterogeneous hybridization of fishes. The 

 egg of Fundulus heteroclitus is employed, while the distinct 

 genera, Menidia, Ctenolabrus, and Stenotomus have served as 

 the male parent. In fertilization the male (Menidia) chromo- 

 somes have been shown by Moenkhaus to be properly formed, 

 and to persist in later stages. From the egg arises an embryo, 

 which is however defective with cyclops eye, small head, 

 pigment not distributed over the blood-vessels, and circula- 

 tion not established though the heart is formed. The pig- 

 ment-cells, red and black, are those characteristic of the 

 female parent ; red pigment not being present in any of the 

 forms used as males. It appears, however, that the red pig- 

 ment may be transmitted by the sperm, since in the reverse 

 cross of Menidia $ x Fundulus o* it appeared in two cases. 



It does not seem possible at this moment to say whether 

 the total failure of the male characters to appear in these 



1963 H 



