Manchester Memoirs, Vol. 1. (1906), No. 6. 3 



{c) Deuterotoky. 



Both sexes are produced as in some species of 

 Tenthredinidae. (Deuterotoky also occurs in 

 the next division — Heteroparthenogenesis). 



3. HeteropartJienogenesis (Henneguy). 



Parthenogenesis in which there is an alternation of 

 generations, a cyclical alternation of sexual 

 and parthenogenetic forms. This may be either 



{a) Regular as in the Cynipid^e and Aphidae, or 

 ib) Irregular as in some species of Tenthredinidai and 

 in the Psychidae. 



Under a fourth head Pcedoparthenogenesis, Henneguy 

 places that rare form of parthenogenesis in which young 

 are produced by the immature insect, which may be either 

 the larva or the pupa. This phenomenon occurs in a few 

 Diptera (Cecidomyidae and Chironomidae) and is usually 

 termed Paedogenesis. I prefer that this term should be 

 retained, and as this is an extremely specialised form of 

 parthenogenesis, it should not be classified with the other 

 forms. 



It is impossible at the present stage of enquiry to 

 make a satisfactory classification of parthenogenesis from 

 a cytological point of view. Marchal (60) and Loisel 

 have each brought forward classifications, which include 

 those cases found in other groups of animals. The results 

 which we have so far appear to indicate that partheno- 

 genesis is equivalent to internal agamogenesis. 



In this summary only those insects in which the 

 maturation of the parthenogenetic ovum has been studied 

 will be considered. The chief feature of these cytological 

 changes which occur is the formation and fate of the polar 

 nuclei. 



