106 CONCLUDING REMARKS. 



Amongst the Mollusca also, phenomena occur, which indicate 

 the possibility of a Parthenogenesis ; thus amongst others, Vogt 

 was able to observe the commencement of development in the 

 eggs of a female Firola laid without fertilization, namely a seg- 

 mentation of the yelk proceeding to a certain extent*. 



From these intimations, it appears that reproduction by Par- 

 thenogenesis is far from being sufficiently exhausted by my 

 investigations, and is still capable of receiving many an addition. 

 Even now, however, we may declare that the hitherto generally 

 admitted proposition of the fecundation theory, that the deve- 

 lopment of the eggs can only take place under the influence of 

 the male semen, has suffered an unexpected blow by Partheno- 

 genesis. It has indeed been attempted to avoid this, and hold 

 on to the old important proposition of the theory of fecundation, 

 by supposing that in many cases a single fecundation may act 

 through several generations ; but much is not gained by this new 

 proposition, as by it many of the phenomena occurring with 

 Parthenogenesis can by no means be explained. On the other 

 hand, it may appear too bold to assign already to Partheno- 

 genesis a definite position in the history of the reproduction of 

 animals, before it is thoroughly explored to a much greater extent 

 and in all directions. Victor Carus has attempted to bring Par- 

 thenogenesis into combination with the care of the brood (Neo- 

 melie),and has established the proposition f: the female form must 

 be fertilized, and indeed by the male form, but for the develop- 

 ment of the latter J no repetition of the fecundation is required, 

 the male germ developes itself in the manner of a bud or nurse. 

 This proposition, however, cannot be applied to all the cases of 

 Parthenogenesis cited by me ; properly speaking, it only suits 

 the Bees ; in the other cases only females are evolved from the 

 unfecundated germs, and in Bombyoc Mori, females and males 

 simultaneously in indefinite numerical proportions. 



In Psyche Helix, Solenobia clathrella and lichenella, in oppo- 



1820, p. 146. " Quoique je ne doute pas qu'il n'y ait des males dans cette espece 

 comme dans les precedentes, je dois annoncer que dans le petit nombre d'indi- 

 vidus que j'ai trouves, ou eleves, je n'eii ai reconnu aucun." 



* See Vogt's Bilder aus dem Thierleben, 1852, p. 21?. 



f System der thierischen Morphologic, 1853, p. 280. 



J Op. cit. p. 57. 



