SHORTER ARTICLES AND DISCUSSION 



MORE EYELESS CLADOCERA 

 Just before a note appeared in Science (Vol. 53, pp. 462- 

 463, May 13, 1921) concerning an eyeless cladoceran individual 

 (a Simocephalus exspinosus), two additional eyeless daphnids 

 occurred in another species of the experimental stock at the 

 Station for Experimental Evolution. These were among off- 

 spring of some Moina rectirostris which were being subjected 

 to crowding in a sex-control experiment (10 mothers in each 130 

 c.c. wide-mouthed bottle containing about 75 c.c. of culture 

 medium). While these two eyeless young were released on suc- 

 cessive days and possibly in separate bottles, they were in bottles 

 which belonged to the same series and received the same treat- 



The precise identity of the mother of neither eyeless young 

 could be determined (since there were 10 mothers producing 

 parthenogenetie young in each bottle), but it is certain that 

 the mothers were normal-eyed and were sisters, or came from 

 mothers which were sisters. All of the mothers' collaterals, 

 which were examined, approximately 250, had normal eyes. 

 302 other young, produced by the 10 mothers in the bottle in 

 which the second of these eyeless appeared, Avere normal. In 

 all about 5,953 young were microscopically examined— a few 

 of which were presumably sisters of the eyeless individuals and 

 the others of which were young from sisters of the mothers of 

 the eyeless individuals. All were normal-eyed. 



One of these eyeless individuals produced 5 broods, contain- 

 ing in all 66 young, all normals. The other produced 4 broods, 

 containing 38 individuals, all normals. 841 offspring of daugh- 

 ters of the one eyeless, and 412 offspring of daughters of the 

 other eyeless were found to have normal eyes. All examined 

 among the collaterals of the eyeless individuals, 5,953 in all, 

 and 1,357 direct first and second generation descendants of 

 the eyeless mothers themselves— a total of 7,310— were normal. 

 Hence despite the fact that there were two eyeless individuals 

 produced by sisters (or by individuals whose mothers were 



seen under the microscope only a single similar individual had 

 568 



