VII PARTHENOGENESIS 267 



sexes) such as " Amphotoky " ; and the terms need 

 not be limited to parthenogenetic cases. In his con- 

 cluding remarks, whilst repeating the expression of 

 his conviction that parthenogenesis will be found 

 more and more to be of frequent and fixed occurrence 

 in various classes of animals, Siebold alludes with 

 caution to the list of cases in which parthenogenesis 

 is stated to occur, given by Gerstaecker in Bronn's 

 Classen und Ordnungen des Thierreichs. Ger- 

 staecker rightly enough distinguishes cases in which 

 parthenogenesis has been observed as an accidental 

 and rare exception, and those in which it has a 

 definitely recurring place. Siebold considers (and 

 after the great pains he has himself expended on the 

 cases recorded in this book, he is fully warranted in 

 so doing) that many of the examples put forward by 

 Gerstaecker require a more careful testing, and he 

 offers some remarks on parthenogenesis in the gall- 

 flies, and in the silkworm moth. Finally, he alludes 

 to cases among Vertebrates in which indications of a 

 power of development in the egg, independent of the 

 male element, have been observed. The most remark- 

 able of these is that quoted by Leuckart in his work 

 already cited, which Siebold omits here, but has done 

 justice to in the short supplementary paper read at 

 the Munich Academy since the publication of this book. 

 In 1844 Professor Bischoff found ova in the uterus 

 of an unimpregnated sow, which exhibited segmenta- 

 tion of the yelk, some into two and four, and others 

 into sixteen and twenty divisions. Other cases here 

 given are as follows : In the oviduct of a three-year-old 



