History of ike Theory of Heredity. 65 



Aphilothrix seminationis. Apbilothrix quadriliniatus. 



Aphilotlirix margiiialis. Aphilothric albopuiictata. 



These are all of them insects which form galls on oak 

 leaves, but Adler finds that the same power to lay par- 

 thenogenetic eggs exists in some other wasps. Pteroma- 

 lus puparum lays its eggs in the bodies of butterfly 

 larvae, and thus gives birth to both males and females. 

 The sexes are so different that there is no difficulty in 

 separating them as soon as they are born. Adler found 

 that females which were thus isolated, and which were 

 shown by microscopic examination to be virgins, never- 

 theless laid eggs as soon as a caterpillar was furnished- 

 them. 



Among 206 females which hatched from these eggs 

 there were only 9 males, so that there is, in this species, 

 a strong tendency for parthenogenetic eggs to produce 

 females. 



In the rose-gall-wasps Adler finds that the males are 

 very rare, about one to fifty females, and he believes 

 that they are superfluous, since the females in two 

 species, Rhodites rosce and Rhodites eglanterim are 

 perfectly parthenogenetic, giving rise to parthenogenetic 

 female offspring. 



The instances of parthenogenesis in larval or imma- 

 ture insects are extremely interesting, but as they will 

 be referred to at some length in another place I 

 will not dwell upon them at present, as the cases which 

 have been given are enough for our purpose, which is 

 simply to show the satisfactory and exhaustive charac- 

 ter of the proof that unfertilized eggs do in many ani- 

 mals develop and give rise to organisms which are in all 

 respects like those born from fertilized eggs. 



In Nematus ventricosus the males are not uncommon, 



