410 LECTURE XVIII. 



in the perfect oviparous females has appendages called spermatheca 

 and colleterium ; and Reaumur might have even appealed to the 

 microscope in support of his idea, for he might have detected, by its 

 aid, spermatozoa in the spermatheca. But this would not have proved 

 the hermaphroditic structure ; for the spermatheca receives the intro- 

 mittent organ of the male, and retains the semen in store for the suc- 

 cessive impregnation of the ova as they pass out ; the ova at the same 

 time being coated by the adhesive and protective matter of the collete- 

 rium. These appendages of the vagina are found in most oviparous 

 insects ; and the true male Aphis is as well known now as that of any 

 other species of insect. Moreover, it is found that the viviparous virgin 

 larvse of the Aphides have not got a trace of those appendages of the 

 vagina, which Reaumur supposed to be male organs. They were not 

 required in her mode of generation, and are not developed. The germ- 

 cell already exists in her, with sufficient spermatic and plastic force for 

 its development ; no semen, therefore, was required to be retained, 

 and there is no spermatheca : the embryonic development is completed 

 in utero, and no secretion for the protective covering of ova was 

 needed. The structures, therefore, which Reaumur, under a miscon- 

 ception of their nature, cited in order to solve the problem of the 

 alleged virgin procreation, are present only in that perfect form of 

 Aphis where no such phenomena ai'e manifested. 



Leon Dufour,* whose extent of research and comparison of the 

 generative organs of insects led him to a true appreciation of the 

 nature and function of the appendages to the female organs of the 

 oviparous Aphides, referred the phenomena of the generation of 

 the larviparous Aphides to " spontaneous or equivocal generation." 

 Now, if we consider what we actually learn from these words, — that 

 the larvae produced by the virgin Aphides are produced by " spon- 

 taneous" or equivocal generation, — it will seem to be little more 

 than another mode of stating the fact. The condition or mode of 

 the fact, the phenomena rendering it possible, are not explained by 

 them ; M. Leon Dufour, however, meant to record his belief in a 

 hypothetical mode of generation, in which, as he expresses it, " the 

 act of impregnation was in no degree concerned." Having detected 

 the male Aphis, and well scrutinised the structure of its organs, 

 having witnessed the coitus with the winged female, and carefully 

 excluded the male in repeating the observations and experiments of 

 Bonnet, M. Dufour satisfied himself, and affirmed, that impregnation 

 had no share whatever in the phenomena of the development of the 

 larval aphis in the body of another virgin larval aphis. 



* CCLVII. 



