128 CARNEGIE INSTITUTION OF WASHINGTON. 



was a significantly higher proportion of degenerating fetuses in preg- 

 nant white females than in non-whites. White cats are not common, 

 and the chance of obtaining pregnant animals is, therefore, not great. 

 Nevertheless, 84 embryos have been observed in such females, and of 

 these 10, or 10.64± 1.86 per cent were degenerating. In 505 embryos 

 of non-white females, 18, or 3.44=^0.51 per cent were degenerating. 

 The difference is 4.02 times its probable error. The conclusion is war- 

 ranted that a significantly greater number of degenerating embryos are 

 found in white than in non-white female cats. Since the sires of these 

 litters were probably, in the great majority of cases, non-white, it is 

 likely that, in some ivhite females at least, a lethal action of some sort is 

 operative when the factor for white is present even in a simplex condition. 



Eyelessness in Cladocera. 



Many cave animals are eyeless. The most satisfactory explanation 

 of this relation is that an eyeless mutation occurred in such species 

 before they became cave inhabitants; that the eyeless descendants of 

 such mutations were able to take advantage of caves and survive in 

 them. Cases of eyeless sports are, accordingly, of special interest to 

 us. In 1919 an eyeless Simocephalus exspinosus was observed from 

 one of Dr. Banta's cultures, but she had, unfortunately, already been 

 killed. This year two eyeless Moina rectirostris appeared in the cul- 

 tures, lacking the optic ganglion as well as the ommatidia, and having a 

 head-form that was changed accordingly. Many young were obtained 

 from each of these individuals and all possessed fully developed optic 

 structures. Likewise, more than 5,000 sibs and descendants of the 

 eyeless individuals were examined. All possessed eyes. Obviously 

 these two cases were merely accidents in development. Since, how- 

 ever, eyelessness is inherited in Drosophila, it seems justifiable to con- 

 tinue the search for eyeless Cladocera. 



Clones in Cladocera. 



A study b}^ Dr. Banta, as yet uncompleted, seems to indicate that 

 the obviously different forms of Simocephalus serrulatus which he has 

 found in different parts of the United States may be further differen- 

 tiated into clones differing by more minute physiological or morpho- 

 logical characters. This matter has been more fully worked out for 

 strains of Daphnia pulex, in which at least three distinct clones, for- 

 merly unsuspected, were differentiated from our laboratory stock. 

 The recognition of additional clones in this material probably depends 

 merely upon a further refinement of our measurement and observations 

 of the different strains. This work is to be carried further. 



Genetic Basis of Animal Behavior. 



Heredity of behavior in dogs. — As stated in the last report of this 

 Department (Year Book, 1920, p. 137), we have undertaken a study 



