32 MANUAI. OF ZOOLOGY. 



known as segmentation of the yelk. Moreover, ova are almost 

 invariably produced by a special organ, or ovary. 



As examples of parthenogenesis we may take what occurs in 

 plant-lice (Aphides) and in the honey-bee; but it will be seen 

 that in neither of these cases are the phenomena so unequiv- 

 ocal, or so well ascertained, as to justify a positive assertion 

 that they are truly referable to parthenogenesis in the above 

 restricted sense of the term. 



The Aphides, or plant-lice, which are so commonly found 

 parasitic upon plants, are seen towards the close of autumn to 

 consist of male and female individuals. By the sexual union 

 of these true ova are produced, which 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 viviparously a brood of 

 young which resemble themselves ; and this second generation, 

 in like manner, produces a third, — and so the process may be 

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

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

 parous 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 from which the young of the viviparous Aphides 

 are produced are variously regarded as internal buds, as " pseud- 

 ova" {i.e., as bodies intermediate between buds and ova), and 

 ^s 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 produce in 

 their interior are true ova, then the case is one of genuine par- 

 thenogenesis, for there are certainly no males. The case might 

 still be called one of parthenogenesis, even though the bodies 

 from which these broods are produced be regarded as internal 

 buds, or as " pseudova;" for a true ovum is essentially a bud. 

 If, however, Balbiani be right, and the viviparous Aphides are 

 really hermaphrodite, then, of course, the phenomena are of a 

 much less abnormal character. 



In the second case of alleged parthenogenesis which we are 

 about to examine— namely, in the honey-bee— the phenomena 



