426 Miscellaneous. 



history of a frail gnat, — a Cecidomyia, which, by pricking the floral 

 envelopes of the birch, causes an irritation productive of tissue, a 

 vegetable hypertrophy, in one word a gall, the cradle of its young. 

 But by the law of parasitism their domicile is invaded by two usurpers 

 whose mission it is to repress the too great multiplication of the 

 Cecidomyia. 



One of these usurpers is a Hymenopterous insect of the genus 

 Misocampus ; — it divines, in this hermetically closed gall, the presence 

 of the quiet larva of the Cecidomyia, and by means of an invisible 

 oviduct introduces an egg into its entrails. From this egg is hatched 

 a gnawing worm, destined to take its nourishment from the living 

 tissues of its victim. The latter, although bearing in its bosom this 

 germ of destruction, continues to devour the substance secreted by 

 the walls of its gall, and the work of assimilation becomes more active 

 in consequence of the consumption of the parasite. But when the 

 time of the metamorphosis arrives, the larva of the Cecidomyia wants 

 the materials necessary for the completion of this great operation, 

 whilst the larva of the Misocampus redoubles its nutritive energy in 

 order to insure its transformation, which is accomplished on the corpse 

 of its victim. 



The second usurper of the gall belongs also to the Hymenoptera, — 

 it is an Eulophus ; this time, however, it is no longer a single worm, 

 but a flock of ten or a dozen famished larvae, which consume the food 

 of the Cecidomyia and consequently that of its parasite the Miso- 

 campus. 



Let us now exhibit another kind of parasitism, that of larvae finding 

 their nourishment in the bodies of living perfect insects ; and see how, 

 confined in a prison destitute of communication with the external air, 

 they are enabled to breathe. 



By dissection in water these parasitic larvae are usually detached ; 

 all that can then be proved by the lens, through the transparent skin, 

 is the existence of ramified tracheae, and consequently the circulation 

 of air through all the tissues. The problem to be solved therefore 

 was the mode in which this air was inhaled, with the condition of a 

 hermetically sealed prison. Dry vivisection has at last revealed to 

 me this mystery. 



In 1827 I published the history and iconography of the metamor- 

 phoses of a fly, the Ocyptera bicolor, the larva of which lives in the 

 abdomen of a Hemipterous insect, the Pentatoma punctipennis. It 

 is not within the viscera that it passes its larva state ; it is always 

 found outside the intestinal canal, and is nourished at the expense of 

 the adipose and other tissues of the Pentatoma. I satisfied myself, 

 that by means of a long, somewhat membranous, caudal tube, termi- 

 nated by a double hook, it had appropriated one of the stigmata of 

 its host. By this organic usurpation, it attained the easy and com- 

 plete exercise of respiratory action. 



Ten years later, I made known the larva of a Dipterous insect, the 

 species of which is still undetermined, which lived as a parasite in 

 the abdominal cavity of the Andrena aterrima. This larva had not, 

 like the preceding, seized upon one of the stigmata of its host, but, 



