﻿18 NINTH ANNUAL REPORT 



IT PRESENTS A FORCIBLE EXAMPLE OF ARREXOTOKY. 



Parthenogenesis, or the production of offspring by virgin females, 

 has long been recognised as a zoological fact, occurring with many of 

 the lower forms of animal life, and not unfrequently with insects. 

 With many of the latter, e. cj.^ the plant-lice, as we have so fully seen 

 in these Reports in the case of the Grape Phylloxera, it is the normal 

 form of reproduction ; while with many other insects, as with some, 

 and perhaps with most gall-flies (6'yn?-^^\f(:«), it occurs regularly at 

 every alternate generation. It also occurs occasionally with insects 

 which normally cannot or do not multiply without direct sexual inter- 

 course, as ill the common Mulberry Silk-worm. As I have remarked 

 elsewhere : * " What in some species is the exception, becomes the 

 rule in others, of which the hive-bee is an example. The male element 

 may be said to possess all degrees of potency in its influence on the 

 reproductive functions of its immediate issue, as the embryo in ova 

 not directly fecundated, attains all degrees of development before 

 death. In cases of parthenogenesis it is potent enough — vital enough, 

 to cause full development of the offspring for one or more generations, 

 though in the majority of instances, and especially where this mode 

 of reproduction does not occur as a rule, this off"spring is most fre- 

 quently male." In other cases females instead of males are produced. 

 The power possessed by the virgin females of certain species to pro- 

 duce male offspring, has been called Arrenotoky by Leuckart; while 

 the parthenogenetic production of females has been designated as 

 Thelytoky by Siebold, who has elaborately shownf that our Imported 

 Currant Worm possesses the former power, and that the unimpregnated 

 eggs hatch into larvas which produce male flies. Further, that this is 

 the rule with all its eggs non-impregnated, which seem to hatch fully 

 as well as those which are impregnated. This power, as Siebold 

 shows, had been observed as far back as 1831, by Kobert Thom, who, 

 in Loudon's Gardener Magazine (Vol. VII, p. 196), states, that "the 

 ova of the female produce caterpillars, even when the male and female 

 flies are kept separate ;" but who, loth to believe in anything so extra- 

 ordinary as lucina sine concuhitu must have seemed in those days, 

 thought that there was " reason to suspect that there is a connection 

 between the male and female caterpillars," from the fact that these, 

 as is so often the case with the Saw-fly larvjie, are not unfrequently 

 found with their tails curled around each other. Thus arrenotoky 

 occurs in our Currant Worm (Fam. TenthredinidcB)^ as it does in the 

 Hive-bee (Fam. Apidm). It is also known to occur among wasps 



*Am. Naturalist, Vol. VII, p. 520. 

 iBeitr. zur Parthenogenesis, ^c, 10(5—130. 



