264 PARTHENOGENESIS VII 



conditions affecting their development and extinction. 

 It occurred to Siebold that an objection might be 

 urged against parthenogenesis in Apus, in that, 

 although he examined consecutive generations and 

 found them always female, he could not be sure that 

 males had not been present before he took his speci- 

 mens, and had not died and decomposed after having 

 fertilised the females. To meet such an objection, he 

 firstly made himself thoroughly acquainted with the 

 male generative organs and the spermatozoa, and 

 secondly with the ovaries and their development. He 

 found the spermatozoa to be motionless like those of 

 other Crustacea, and he never succeeded in detecting 

 any of them in the female genitalia amongst the 

 specimens belonging to supposed female generations. 

 But he equally failed to find spermatozoa or a recep- 

 tacle for them in the female genitalia of the specimens 

 of mixed generations, and therefore no conclusion 

 could be drawn from the observation. The structure 

 and development of the ovum, however, made this 

 observation decisive, since it was found that an egg- 

 shell forms round the ovum in the uterus, and, in the 

 absence of a micropyle, fertilisation, if it takes place 

 at all, must be accomplished before this shell is hard- 

 ened. A further proof of another kind was obtained 

 by experiment. Having removed eggs from females, 

 which certainly at the time contained no spermatozoa, 

 Siebold placed them in a small tank, and from these 

 obtained Apus-embryos. Others were reared to matur- 

 ity from eggs taken in the pond. 



The relative size of male and female is a question 



