196 THE BIOLOGY OF INSECTS 



Eastern tropics — known as Termitoxenia and Termitomyia 

 — from whose life-history the whole larval and pupal stages 

 are omitted, for according to their discoverer, E. Wasmann 

 (i90i),the former lays a relatively enormous egg whence a 

 developed adult is hatched, while the latter gives birth to a 

 single offspring already in the adult form. It is remarkable 

 that such extreme abnormalities of life-history as these 

 should occur among insects of that order (the Diptera) in 

 which the ordinary course of transformation has become 

 most elaborated with the most profound difference between 

 adult and larva. 



While in these insects the preparatory stages are largely 

 or wholly omitted from the life-cycle, there are other 

 Diptera in which young may be produced by lar/ae or pupae, 

 so that insects not adult have the power of reproduction ; 

 these furnish examples of " paedogenesis " or precocious 

 parenthood. More than half a century ago O. Grimm 

 (1870) saw female pupae of the midge Chironomus lay eggs 

 which gave rise to active larvae ; we have seen that a typical 

 insect pupa is closely like an adult in essential features of 

 form, so this exceptional occurrence might be regarded as 

 a somewhat surprising instance of virgin reproduction. 

 Five years earlier, however, N. Wagner (1865) had noticed 

 that within a grub of certain gall-midges (Cecidomyidae) a 

 number of smaller larvae might be seen, these ultimately 

 making their way out to free life through the body-wall of 

 their larval mother. It is now known, as stated by W. Kahle 

 (1908), that these abnormal young are developed from eggs 

 which break loose from the ovaries already present in the 

 parent hrva, and float in the body-cavity, where they 

 segment and form embryos, which develop into the larvae 

 that burst out of the parent's body. After a succession of 

 these larval families young are produced that complete their 

 transformation into pupae and adults, so that the whole 

 cycle is made up of a sexual generation alternating with 

 a number of virgin larval generations such as is normal 

 in several groups of animals, notably in certain parasitic 

 worms. 



