236 EDITH PINNEY 



No evidence of paternal inheritance in this cross has been 

 observed. Only one individual capable of hatching has been 

 reported, but development to an advanced stage is common. 

 Since hatching occurs so rarely, one would hardly expect in a 

 study of fixed material to find the conditions which precede 

 perfect development predominating, and it is probable that all 

 of the conditions so far described are to be correlated with the 

 pathological characters of those defective embryos which show 

 only maternal inheritance. That retardation during cleavage 

 is correlated with the delayed division of some of the chro- 

 mosomes is quite certain. Newman ('15, '17) emphasizes the 

 importance of retardation in development as a factor in the 

 formation of pathological embryos. The conditions of lagging, 

 the time at which it first appears, and the extent to which it 

 involves the nuclear material may be as variable as the patho- 

 logical characters which it entails. 



Ctenolabrus adspersus 9 X Fundidus heterodiius cf 



In view of the facts observed in Fundulus eggs fertilized by 

 the sperm of Ctenolabrus, which produce larvae showing only 

 maternal characters, it seemed of interest to examine the recipro- 

 cal cross in which development is less successful, in that none of 

 the eggs survive gastrulation. I have made this cross six times 

 with practically the same results. Usually about 75 per cent of 

 the eggs were fertilized, although the ratio of eggs which cleaved 

 regularly to those that cleaved irregularly because of polyspermy 

 varied. 



Cleavage resulted in the formation of a blastoderm which 

 extended well over one side of the egg, but there was no evidence 

 of a germ ring. In one experiment in which the eggs were ex- 

 amined eighteen hours after fertilization, the blastoderms had a 

 diameter almost equal to that of the yolk, and all showed an 

 opaque spot at one side which suggested that the region where 

 gastrulation began had been the first to succumb. Figure 26 

 shows a section through a blastoderm of a hybrid which was 

 fixed fifteen hours and forty-five minutes after fertilization. 



