314 POLYEMBEYONY AND THE DETERMINATION OF SEX. 



the discoidal form through compression of its surfaces from opposite 

 sides; it afterwards takes a reniform shape, as the result of the 

 appearance of a deep hilum, which grows from above downward 

 and corresponds to the dorsal region, while the convex surface 

 opposite to the hilum corresponds to the ventral face. This very 

 characteristic form generally shows itself by the 25th of May (H. of 

 the spindle tree). Finally, about the 10th of June, the embryos 

 have reached the larval state, and the chains of Encyrtus have reached 

 their full length and present the characteristic form described at 

 the beginning of this article. 



The most striking fact in the development of Encyrtus is, then, 

 that a single egg deposited within the egg of the moth proliferates 

 by division of the nucleus in such a manner as to form a certain 

 number of plurinuclear masses, and that these, dividing in their 

 turn, produce as many morales as there will be embryos in each of 

 the chains. 



Polyembryony being, as appears from what precedes, the ordinary 

 mode of development of E. fuscicoUis, it may be foreseen that the 

 study of the Chalcidids, particularly of the group of Encyrtids, 

 will result in the discovery of other analogous cases. 



Marchal already cites Encyrtus testaceipes Ratz., a parasite of 

 LithocoUetis cramereUa^ leaf -miner of the oak. He could not see, 

 it is true, more than the advanced stages of the development of this 

 species, the observation having been made in October. The larvae, 

 to the number of 12 to 15 in a caterpillar, had for the greater part 

 already formed their cocoon; but in some caterpillars the parasites 

 were grouped in an epithelial tube similar to that of E. fuscicollis. 

 The structure of the tube being absolutely the same, there is no doubt 

 that development takes place in the same manner. 



According to Giard (1898, Bull., p. 127-129) Litomastix trunca- 

 tellus Dalm. {C O'pidosoma Mayr), may present an embryonal multi- 

 plication of the most active kind. Close to 3,000 of these insects can 

 succeed in developing from a single caterpillar of Plusia gamma L., 

 whilst the number of eggs contained within the ovaries of the female 

 does not exceed a hundred."^ 



Another case of polyembryony was observed by Marchal in Polyg- 

 notus TTiinutus Lindeman {Platygaster) , a minute parasitic Proc- 

 totrypid (length ^ mm.) of the Ceciclomyids of wheat and oats {G. 

 destructor Say and avence Marchal). The embryos, which one finds 

 to the number of 10 to 12 in the gastric sac of the Cecidomyia larva, 



a Howard (1892, p. 582), who counted 2,500 specimens of Litomastix trun- 

 catcUtis which had issued from one caterpillar of Phisia brassicw Riley, cal- 

 culated the number of eggs contained in the ovaries of the female in the 

 vicinity of 160 (the maximum 300). 



