342 



ON VIVIPARITY IN POLYCTENIDiE. 



By K. Jordan, Tring. 



(Text-figs. 9, 10, II.) 



The methods of the production of offspring in insects may be 

 classified under the two headings Oviparity and Viviparity. 

 In the former case the offspring leaves the ovary and body of 

 the mother as an egg from which the larva emerges after ovi- 

 position, while in viviparous insects the offspring is deposited 

 as a larva or a chrysalis. Viviparity, however, really comprises 

 two very different kinds of reproduction. In Gonochetal Preg- 

 nancy (Heymons) the ovar}^ produces an egg which is retained, 

 in the oviduct until it has ripened into a larva or even a pupa. 

 This may occasionally also happen in insects which are normally 

 oviparous. In Ovarial Pregnancy, on the other hand, the 

 germ remains in the ovarial tube where it originated, and 

 gradually matures here into a larva without an intermediary 

 egg-stage. Ovarial Pregnancy is comparatively very rare. It is 

 known to occur among Aphides, Cecidom^àids, Chrysomelid 

 beetles, etc., the best and perhaps most interesting example 

 being that of Heminierus, the pecuhar blind, aberrant earwig 

 which is found in Africa on Cricetomys gamhianus, a kind of rat. 

 According to Heymons (1909) the ontogeny of Heminierus is 

 distinguished by the absence of yolk from the egg-cell, and the 

 presence of an amnion by means of which the embryo derives 

 nutriment from the surrounding tissues of the ovarial tube, 

 this method of nutrition of the embryo being unique among 

 insects. At a later stage, when the embryo changes from the 

 inverted position (ventral side convex and dorsal side concave) 

 into the imaginai position (ventral side concave and dorsal 

 side convex), the amnion disintegrates and is replaced, functionally, 

 by a special organ projecting from the neck, the vesícula cephalica 

 (Heymons), which osmotically sucks up the disintegrating 



