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 larvse 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 

 Muscidas 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 [369] this myself in 1864 in a large species of 

 Petasia in Palestine, and published an account of the pheno- 



Bibliography : 



369. LOWNE, B. T., ' Observations on Immature Sexuality and Alternate 

 Generation in Insects.' Trans. Ent. Soc., Lond., vol. 1871, pp. 193- 

 202. 



