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114 ELEMENTS OF BIOLOGY. * 



close of autumn to consist of male and female individuals. 

 By the sexual union of these, true ova are produced, which 



Fig- 34.— Bean Aphis {Aphis fabm)y winged male and wingless female. 



remain dormant through the winter. At the approach of 

 spring these ova are hatched; but instead of giving birth to 

 a number of males and females, all the young are of one 

 kind, variously regarded as neuters, virgin females, or 

 hermaphrodites. Whatever their true nature may be, these 

 individuals produce viviparoicsly a brood of young which 

 resemble themselves ; and this second generation, in like 

 manner, produces a third, — and so the process may be re- 

 peated, for as many as ten or more generations, throughout 

 the summer. When the autumn comes on, however, the 

 viviparous Aphides produce— in exactly the same manner — 

 a final brood ; but this, instead of being composed entirely 

 of similar individuals, is made up of males and females. 

 Sexual union now takes place, and ova are produced and 

 fecundated in the ordinary manner. 



The bodies irom which the young of the viviparous 

 Aphides are produced are variously regarded as internal 

 buds, as "pseudova" (z>., as bodies intermediate between 

 buds and ova), and as true ova. 



Without entering into details, it is obvious that there is 

 only one explanation of these phenomena which will justify 

 us in regarding the case of the viviparous Aphides as one 

 of true parthenogenesis, as above defined. If, namely, the 

 spring broods are true females, and the bodies which they 



