34 D. B. CASTEEL AND E. F. PHILLIPS. 



thenogenetically is of far more use to a species where gamic 

 reproduction is unnecessary, since fertilization is not necessary to 

 give a stimulus to the egg so that it may develop, and what the 

 species loses in lack of cross fertilization is more than made up 

 in the advantage it has through its parthenogenetic power. 

 Since then arrenotoky is the least specialized form of partheno- 

 genesis, and since a crossing does occur at every second genera- 

 tion in species with this power, it follows that according to the 

 theory of germinal variation we would find more variation in 

 arrenotoky than in either thelytoky or amphoterotoky. In fact 

 the decrease in variability would not be very great, since in 

 every case but one half the crossing is dispensed with. 



Variation in parthenogenetic forms has been observed previ- 

 ously. Weismann l found that the parthenogenetic ostracod, 

 Cyprus reptans, showed variation, and Warren 2 found consider- 

 able variation in Daphnids. Both of these cases fall under 

 amphoterotoky, so that on a priori grounds we would expect 

 still more variation in arrentoky. It is also held by some that 

 males tend to vary more than females, and perhaps this tendency 

 has something to do with what we find in the case examined. 

 Davenport and Bullard, 3 found 2^4 per cent, more variation in 

 males than in females in swine. Darwin 4 gives a considerable 

 number of cases showing the same tendency, and others have 

 observed similar facts. On the other hand there are cases in 

 the Odonata (Gouiphus and Macrothemis, Calvert 5 ) and in the 

 Lepidoptera (Thy re us abbotii, Field 6 ), in which the females are 

 more variable than the males so, that we must not assume too 

 much on this ground. 



This still leaves considerable variation in drones to be accounted 



1 Weismann, A., "The Germ-plasm," 1893. 



2 Warren, E., "An Observation on Inheritance in Parthenogenesis," P. R. Soc. 

 Lond., Vol. LXV., pp. 154-8, 1899. 



3 Davenport, C. B., and Bullard, C., " Studies in Morphogenesis," VI. "A con- 

 tribution to the quantitative study of correlated variation and the comparative varia- 

 bility of the sexes." Proc. Am. Soc., Vol. 32, pp. 85-97, 1897. 



4 Darwin, Charles, "The Descent of Man." London, 1871. 



5 Calvert, P. P., "The Odonate Genus Macrothemis and Its Allies," Proc. Boston 

 Soc. Nat. Hist., Vol. 28, pp. 301-332, 1898. "On Gomphus fraternus, externns and 

 crassus (Order Odonata)," Entomol. A r eios, March, 1901. 



6 Field, W. L. W., " A Contribution to the Study of Individual Variation in the 

 Wings of the Lepidoptera," Proc. Am. Ac. Sc , Vol. 38, pp. 389-396, 1898. 



