ALTERNATION OF GENERATIONS 245 



Parthenogenesis. 



Parthenogenesis has been defined as the production of 

 new organisms by virgin females, without the intervention 

 of males. Owen, who originated the term, gave it, however, 

 a wider meaning, and applied it to all processes of gemmation 

 exhibited by sexless beings or virgin females. In our 

 opinion Owen's definition is to be preferred, though we 

 would modify it to " all processes of gemmation by 

 temporarily or permanently sexless beings which are always 

 parts of Individuals." 



This is to widen the definition in one direction and to 

 narrow it in another, making it include phenomena which 

 are not usually held to be parthenogenetic, and ruling out 

 the development of the unfertilised female element as not 

 true parthenogenesis. Many, no doubt, would rule out the 

 former and include the latter, but this apart, one thing is 

 obvious, that the term should not be so widely applied as 

 to embrace two such distinct phenomena as the unaided 

 development of the unconjugated gamete or unfertilised 

 ovum, and the production by gemmation of a Hydra zooid, 

 a coral megazooid, or an aphis. 



And for this reason : that in the first cases we are 

 dealing with the abnormal origination of a new Individual, 

 whereas in the second the matter is one of the production 

 of a further portion of an Individual. 



The gamete is a sexual element, but the cell from which 

 arises a neuter aphis can surely not be classed as such. 

 Were it to be so, then each successive neuter aphis would 

 be a new Individual of unusual sort and represent a new 

 generation. We would, in fact, limit the application of the 

 term " Parthenogenesis " to the production of new organisms 

 from cells which are not terminal or sexual cells, but sexless 

 intermediate cells ; the producer of the new organism being 

 part of an Individual, and its product (and antecedent 

 producers, if any) the remainder. 



The development of an unconjugated gamete or an 

 unfertilised ovum is abnormal, and where, as with certain 

 Algae, it occurs in Nature, one is inclined to presume that 

 accidental special factors have interfered to upset the 

 equilibrium of the gamete in the absence of the specific 



