AND ANATOMY OF CERTAIN HYMENOPTERA PARASITICA. 409 



older parasitic larvae was slowly poisoning the unfortiinate host-insect, and 

 so producing the peculiar discoloured unhealthy condition. 



With regard to the question of respiration, there can be no doubt that the 

 tail vesicle is respiratory in function. Seurat (12) thought that while the 

 vesicle might be partly respiratory in function, it was at the same time a 

 locomotor organ. I do not agree with the latter suggestion. Kulagin (16) 

 thought that the vesicle was excretory in function. 



There seems to be a good deal oi: " lipoid " matter in the vesicle cells ; the 

 outer granular cloud acts like the lipoids with fixatives and stains, and this 

 is quite possibly the part of the cell which absorbs oxygen from the blood of 

 the caterpillar. The cell processes on the inner surface of the vesicle cells 

 are possibly a mechanism for increasing the surface of the respiratory cells, 

 and so facilitating oxygen exchange between host and parasite. 



Certain observers have considered that because the very young parasitic 

 larva has no vesicle, the latter cannot be respiratory, for they consider if it 

 were respiratory it would be necessary for, and present in the young. As a 

 matter of fact, this line of argument is not of much value ; many internal 

 parasitic iarvse [Litomastix (13), etc. etc.) have no vesicle or other highly 

 specialized arrangement for collecting oxygen from their host, and have 

 adjusted themselves to their modus vivendi in another way. In oxie sense 

 the larval Microgasteridse are the most specialized of the Entomophaga in 

 that they have the vesicle, but it is more than likely that the larvaa of 

 Litomastix or Encyrtus fuscicoUis (13), which have no vesicle, are really the 

 most highly efficient sort of internally parasitic insect larvse. 



These creatures have solved the respiration problem in some way which 

 does not require any peculiar morphological specialization. Ihe bladder of 

 Microgaster is a makeshift : the ultimate abdominal " segment " has been 

 pushed into a service for which it was never intended. 



The Tachinidse, a family of Dipterous internal parasites of moth and 

 butterfly larvse, go about the problem in quite a different manner — they 

 early become attached to one of the host's main tracheal tubes, so that their 

 own tracheae may take in air by means of the host^s tracheal apparatus : this 

 is a very clever specialization (17). 



Dr. Boisduval (6), in some remarks on the manner of nutrition in the 

 Entomophaga, likens it to that of a foetus. I have in this paper brought 

 forward the evidence of the embryonic membranes which persist for so long, 

 and whose cells become hypertrophied. In a sense Boisduval is correct. 



Attention should specially be directed to the remarkable adjustment in the 

 course of development of the parasitic Apliidius^dinii the life of the host. In 

 some ways the same applies to all Hymenopterous internal parasites of 

 insects. We find that in early life, while the host is comparatively young, 

 the parasites are enclosed in an embryonic membrane; it neither feeds nor 

 defecates. All nourishment is gained by a process of absorption through a 

 cellular embryonic membrane. The life and health of the host is hereby 



