572 [December 



creep out. The development of the latter within the body of the mother lasts 

 8 or 10 days. After .3 or 5 days the same process is repeated within the body 

 of the young larvre. His statements and drawings are so precise and detailed, 

 that it is difBcult to discredit them. Nevertheless the novelty of the discovery 

 (if it is one) is so overwhelming, that it is not generally credited yet. He does 

 not explicitly mention, that his larvse of the second aud LLird generation have 

 the "breast-bone" peculiar to Cecidomyia, but it follows indirectly from his 

 statements. 



There is no doubt whatever in my mind, that the 7 or 10 youno- 

 larvas that crept out of the body of the Cecidomyia larva, were nothing 

 but the larvae of Chakidulse or Proctotrxipulse, several species of which 

 I know from experience to breed in about those numbers inside the 

 bodies of the larvae of Willow Cecidomi/ia. The description of the 

 mother larva being '' half-dead and hardly moving," before they crept 

 out, is to the life, and represents exactly what every breeder of Insects 

 has witnessed a dozen times in the case of ichneumonized larvae. Xn 

 to Wagner's statement that these same newly-born larvae went through 

 the same process a second time, I cannot but believe that it is a pure 

 and simple delusion. If I had found that the Gall-gnats of the Willow 

 were ever infested by Ichneumon-flies or Tachina-flies, I should suppose 

 the above to be a mere case of Secondary Parasites coming out of the 

 bodies of Primary Parasites. But, so far as my experience extends, 

 they are infested only by Cliahulldpe and Procfotrupidse. Now in 11 

 published cases of Secondary Parasites that I am acquainted with, two 

 of which I have myself published, and in several unpublished cases that 

 are known to me, the Primary Parasite is, in every one of them, either 

 an Ichneumon-fly or a Tachina-fly, and never a Chalcidide or a Procto- 

 trupide. Whence I conclude that there are most probably no Seconda- 

 ry Parasites that infest the genus Cecidomyia, because, if there were, 

 they must in all probability, contrary to what seems to be a general 

 rule, be parasitic on a Chalcidide or a Proctotrupide. We are not 

 bound, however, to believe every erroneous or anomalous statement, 

 until we can show how and why the error originated. When, as here, 

 a supposed fact violates a law that prevails throughout Vertebrata and 

 Annulata, and perhaps throughout the whole Animal Kingdom, viz: 

 that it is only the adult animal that propagates its species, the o/ms 

 probandi lies on the asserter of the fact, and not on the rest of the Sci- 

 entific World. It is contrary to experience that lambs, and calves, and 



