56 Heredity. 



vations of a great number of competent naturalists; 

 that the subject lias been thoroughly and carefully 

 studied, with every precaution against error, and that 

 our belief in its existence does not rest upon the unycri- 

 fied statements of a few observers. 



In this sunimaiT I shall give many references to 

 authorities, but as my purpose is not to give a com- 

 plete bibliograph}", but simply to show how thoroughly 

 the subject has been studied, many names are omitted. 



Most of the folio win 2; facts are taken from Ger- 

 staecker's history of the subject in Volume V. of 

 Bronu's Klassen und Ovdnungen des Thierreiclis, 

 although I have referred to many of the original 

 papers and have added many facts which are not 

 mentioned by Gerstaecker. The subject is perfectly 

 familiar to most naturalists, and the amount of space 

 devoted to it may seem unnecessarily great to such jier- 

 sons, but it is important to impress upon unscientific 

 readers a sense of the exact and definite character of 

 the evidence for the existence of parthenogenesis, and 

 a short history of the subject seems the most effective 

 means for accomplishing this purpose. 



Among the Crustacea and insects, parthenogenesis is 

 by no means unusual. It occurs in some groups where 

 impregnation by males is so nearly universal that natu- 

 ralists have been slow to credit any exceptions. In 

 other groups it is the general rule, and fertilization by a 

 male is the exception. In some genera and species the 

 power is shown only by a few individuals, while in 

 others it is shared by all the females. In some cases 

 the unfertilized eggs give rise to females only, in other 

 cases to males, and in still other cases to both sexes. 



In 17T5, Schiiffer, of Regensburg, discovered its oc- 

 currence in fresh-water Crustacea, although Dr. Albrecht 



