250 EDITH PINNEY 



A great deal of irregularity exists among the blastoderms 

 at this period in the number of cells which they contain. While 

 much of this irregularity is, no doubt, the direct result of early 

 abnormalities in cleavage, some of it must be ascribed to the 

 effects of polyspermy. No differences, great enough to be used 

 as a definite basis for correlation with these two causes, can be 

 seen in this material. However, we are justified, I believe, in 

 concluding that the varying degrees of abnormality exhibited 

 in the later stages may be correlated with the variability existing 

 in the earlier cleavages and that both lead sooner or later to a 

 cessation of development. 



Ctenolabras adspersiis 9 X Menidia menidia notata cf 



The cytological features in the Menidia-Ctenolabrus hybrids 

 are in many respects similar to those already described in the 

 Fundulus-Ctenolabrus crosses. Because of the close likeness 

 of the two cases, it will be necessary only to outline briefly the 

 conditions observed. The chromosomal complex of Menidia 

 has been described by Moenkhaus; that of Ctenolabrus has 

 received attention in an earlier section of this paper. From a 

 comparison of the two descriptions it is clear that there can be no 

 hope of recognizing the maternal and paternal chromosomes in 

 these hybrids. As in the crosses between Stenotomus and 

 Ctenolabrus, however, two groups of chromosomes appear on 

 the early metaphase spindles of first-cleavage stages of the cross 

 Ctenolabrus adspersus 9 X Menidia menidia notata cf . No 

 physiological or morphological differences were observed in the 

 two groups. 



Several early cleavage stages were examined, but no abnormali- 

 ties were noted. The earliest anaphase stages studied were 

 from third-cleavage stages. In these the chromosomes divide 

 and pass to the poles in straight ranks with almost diagrammatic 

 regularity. Unfortunately, the sections which were made of this 

 material were not clear enough to permit me to detect minute 

 differences in the shapes of the individual chromosomes, and 

 so I have not attempted to give figures of these early stages. 



