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DEVELOPMENT OF THE GENERATIVE ORGANS. 723 
parthenogenic generation and protandry ; and, although these 
are by no means confined to the Insecta and Trematoda, there 
is no other group of highly-developed organisms comparable 
with the Insecta which exhibit parthenogenesis, and I am not 
aware that any other highly-developed group of organisms 
exhibit protandry, without at the same time exhibiting normal 
hermaphrodism. 
Parthenogenesis—The development of ova without previous 
impregnation is of frequent occurrence in Insects, either as a 
more or less rare phenomenon occurring in otherwise perfect 
females, or as an alternation of generation occurring in imper- 
fect females, which alternate with perfect normal females. 
The latter, which is undoubtedly the normal form of partheno- 
genesis, is supposed by Lubbock to be the result of an acquired 
power of developing young in the larval form, and the pheno- 
menon as it occurs in the larve of Cecidomyia is certainly 
highly suggestive of such an explanation; and I would draw 
attention in this connection to the remarkable similarity of this 
phenomenon and the reproductive process in the larval forms 
of parasitic Trematoda, Cercaria. 
Protandry.—Although in many Insects, as, for example, in 
most Lepidoptera, the ovaries are mature when the insect 
escapes from the pupa, it is more generally weeks or even 
months before the ova are fully matured. In such cases the 
act of sexual union occurs long before the ova are mature. 
Thus the nuptial flight of the Queen Bee occurs in the summer, 
but the ova are not deposited until the ensuing spring. 
The same is general in the social Hymenoptera. In the 
Muscide the act of copulation takes place whilst the ova are 
still very rudimentary; and occasionally, at least in many 
Orthoptera and Hemiptera, it occurs in the larval or nymph 
stage. I observed [869] this myself in 1864 ina large species of 
Petasia in Palestine, and published an account of the pheno- 
Bibliography : 
369. Lownkg, B. T., ‘ Observations on Immature Sexuality and Alternate 
Generation in Insects.’ Trans. Ent. Soc., Lond., vol. 1871, pp. 193- 
202. 
