STERILIZATION OF THE TETTIGID^. 153 



morphological modifications of organic tissue, which 

 may be indifferently the produce of vegetable or of 

 animal excitation. Such like deformations are com- 

 monly connected with some change of function in the 

 parts affected. In the case of some plants the fruit 

 becomes sterilized and altered in structure ; but still it 

 may retain a strong resemblance to the true seed. 

 Sterility brought about through the action of one 

 animal on another, M. Giard designates by the process, 

 '' Castration parasitaire." 



One out of many instances of the excrescences 

 made by homopterous insects, which result in a close 

 imitation of the true fruit, may be seen in the false 

 cones made by Chermes ahietis on the spruce-fir. These 

 are so similar to the true cones that close inspection 

 alone will separate one from the other. Very curiously, 

 the pseudo-fruit of a plant will sometimes imitate not 

 the fruit of the particular plant affected, but that of a 

 species belonging altogether to a different family. 



Leon Dufour long ago pointed out the direct sterility 

 of the flowers of Verhascum and Scrophularia by the 

 action of a Cecidomyia ; and M. Giard shows that a fly 

 of the same family produces a similar efi'ect on the 

 seeds of Hypericum perforatum. 



In 1857 Perris bred parasitic larvae on several 

 Deltocephali, which eventually spun cocoons and 

 matured pupse of Gonatopus pedestris of Dalm. From 

 certain reasons he gives, he concluded that these 

 insects were parasitic on other parasitic forms which 

 had previously attacked the Tettigidse ; and that these 

 larvas still infested them. 



The insects bred by M. Giard from Typhocyha liippo- 

 castani and T. Douglasi ipioYed to be the hymenopterous 

 Aplielopus melanoleucus, Dalman, and the perfect forms 

 were excluded from these sacs towards the end of 

 June. Later in the year, viz., in early October, indivi- 

 duals of a dipterous fly were excluded from other 

 Typhlocybidas of the same species. These proved to 

 be Ateleneura spuria of Meig., of which two generations 



