136 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



a member of the family Chironomidae. A species of the same genus, 

 T. dissimilis, may also reproduce parthenogenetically, eggs being laid 

 by the female immediately upon leaving the exuviae. Should the nearly 

 mature pupa fail to transform, the eggs nevertheless develop, and thus 

 reproduction is also paedogenetic. The eggs are laid in a gelatinous 

 string, the string from each ovary containing about 60 obliquely placed 

 eggs (Johannsen, 1910, 1937). Embryonic development takes place as 

 in Chironomus. 



A complicated case of paedogenesis is presented by the coleopteran 

 Micromalthus debilis in which there are five mature reproductive forms. 

 These are an adult female, a thelytokous paedogenetic female, an 

 arrhenotokous paedogenetic female, an amphiterotokous paedogenetic 

 female, and an adult male. The adult is probably sterile; the thelytokous 

 paedogenetic female is the essential reproductive type, giving rise by 

 parthenogenesis and viviparity to a sizable brood of indeterminate larvae. 

 The arrhenotokous paedogenetic female matures a number of eggs of the 

 potential male type, only one of which is shed. The haploid male arises 

 from no other source. The amphiterotokous paedogenetic female has 

 proved to be essentially a male producer in which the development of the 

 male is arrested and female-producing eggs develop secondarily. The 

 development of this insect was first described by Barber (1913) and later 

 in more detail by Scott (1938). Another striking example of paedogenetic 

 development has been described by Hagan (1931) for the heteropterous 

 bat parasite Hesperoctenes fumarius which is also a viviparous form. An 

 outline of its development is given in Part II. 



Although a large number of parthenogenetic species of insects are 

 also viviparous, there are many viviparous forms that undergo normal 

 reproduction. Hagan (1931) has recently given a summary which with 

 but slight change is reproduced here. 



1. Ovoviviparity . — Viviparity with no nutritional structures, the egg 

 containing sufficient yolk to nourish the young until hatching, e.g., 

 Coccidae, Coleoptera, Sarcophagidae, Chironomidae (Tanytarsus), 

 Cecidomyiidae (Miastor), etc. 



2. Intussuctio-viviparity . — Viviparity with nutritional structure for 

 larva only, the egg having sufficient yolk to nourish the embryo until 

 hatching. The larva is retained in the maternal uterus and nourished 

 by means of specialized organs, e.g., Hippoboscidae, Muscidae (Glossina, 

 Hylemyia) . 



3. Exgenito-viviparity . — Viviparity following haemocoelous develop- 

 ment and fat-body absorption, the embryo obtaining nourishment directly 

 from tissues by means of a trophamnion, trophserosa, or trophchorion, 

 e.g., Strepsiptera, Chalcidae (in polyembryony), etc. 



