Sexual reproduction, which is considered a necessity 

 for the majority of animals, especially the higher ones, is 

 intrinsic also to the plant kingdom, but in the latter it 

 is not so necessary and frequently is changed into different 

 forms of vegetative reproduction. 



Referring to corresponding examples (potato, weeping 

 willow, bulbous plants, and so on), Baer turned to the 

 invertebrates, noting that in them also (for example, in 

 Infusoria, Bryozoa, Ascidia, and polyps) reproduction by 

 division and budding is very usual. Other forms of repro- 

 duction without fertilization, namely parthenogenesis, is 

 characteristic among insects. The main form of partheno- 

 genesis was considered Wagner's discovery of the Miastor. 

 Contrary to the earlier known parthenogenesis, in which the 

 source of ova developing without fertilization was thought 

 to be the sexually mature females, in viviparous cecidia 

 the embryos originate in the organism of the unformed larvae 

 incapable of fertilization, Baer considered it advisable to 

 give this form of reproduction a special name, and by analogy 

 with parthenogenesis he termed it paedogenesis.25 i n both 

 terms, Baer wrote, the first half of the word shows the 

 producing subject. In a footnote he mentioned the correct- 

 ness of Leuckart's note that the word parthenogenesis actually 

 means the genesis o£ a virgin, and not genesis by a virgin; 

 however, as this term became generally used, it was impossible 

 to avoid analogy with it in the formation of a new record. 



Comparing the phenomenon of parthenogenesis in Aphidae 

 with paedogenesis in cecidia, Baer reached the conclusion 

 that, as in Aphidae, the appearance of this or that form of 

 reproduction (with fertilization or without it) is closely 

 related to conditions of existence, in particular to intensity 

 or nourishment; more abundant nutrition aids parthenogenetic 

 and paedogenetic reproduction. The main conclusion to be 

 drawn from the comparison of these forms of reproduction is 

 that they both are an example of alternation of generations, 

 or "alternating reproduction," during which sexual generation, 

 i.e. by means of fertilization, alternates in one or more 

 generations with reproduction without fertilization. To 



25. From the Greek P AIDES, meaning children, 

 476 



