240 BESSIE NOYES 



effective in some cases. In Stylonychia, Middleton ('15) isolated 

 from the progeny of a single individual two strains that differed 

 in the rate of fission; in Difflugia, Jennings ('16) found strains 

 that differed in a number of characters (number and length of 

 spines, diameter of shell, etc.) ; in Centropyxis, Root ('17) isolated 

 strains differing in number of spines and the size of shell; in 

 Arcella, Hegner ('20) found another protozoan that showed the 

 same phenomena, the lines differing in spine number and diame- 

 ter of shell within the same clone. 



In comparison with the mass of experimental data in the 

 protozoa, a relatively small amount of work has been done on 

 forms reproducing parthenogeneticallj'-, although in the species 

 where no reduction in the number of chromosomes occurs, the 

 reproduction is as typically uniparental as in the cases where an 

 organism reproduces by fission. 



Kelly ('13) tried by selection to alter the relation of the third 

 to the fourth antennal joint in a parthenogenetic aphid (Aphis 

 rumicix), but the work was carried on for only two generations 

 and no effect produced. 



Agar ('14) worked with three parthenogenetic Cladocera, 

 Simocephalus exspinosus, S. vetulus, and Daphnia obtusa, and 

 a parthenogenetic aphid, Microsiphum antherinii. In, both 

 species of Simocephalus an attempt was made to increase the 

 body length by selection, but the coefficient of correlation between 

 individuals and their ancestors showed no diminution as the 

 scale of ancestors was ascended, and in Daphnia also there was 

 ''no evidence of inheritance of interclonal variation." In 

 Microsiphum antherinii, however, there was a diminution in the 

 intensity of the correlation from the parental to the grandparental 

 relation, which indicated that selection within the clone had 

 been effective. In a discussion of this part of the work, Agar 

 suggests that such a conclusion must be stated tentatively, 

 since in all the cases the progeny are produced viviparously 

 and have short life histories, so that there is a comparatively 

 short time to eradicate the effects of intra-uterine life. Ewing 

 ('14 a, b, '16) studied various characters of Aphis avenae Fab., 

 and in the first ten generations attempted by selection to increase 



