348 



PARASITISM 



darkness. As the oxygen became used up by the parasite the 

 luminous zone gradually spread outwards until luminosity was 

 only betrayed at the edges of the coverslip, where oxygen was 

 passing into solution from the outside air. By means of this 

 technique it was shown that the tail of Ichneumon larvae performs 

 no apparent function in respiration, the Protozoa grouping 

 themselves entirely in relation to the body of the parasite only. 

 The absence of any proper blood circulation in the caudal 

 appendage appears also to argue against this organ performing a 

 respiratory function. It is probable also that the " tail " of 

 Proctotrypid and Cynipid larvae is likewise devoid of a respiratory 

 function. With regard to the caudal vesicle of Braconids, referred 



Fig. 85. 



Longitudinal section through larva of Apanteles. d, d, Dorsal, 

 vessel, in, Intestine. (Adapted from Grandori.) 



to below, Thorpe's experiments show that where this vesicle is 

 large and supplied with a good blood circulation it is undoubtedly 

 of importance as a respiratory organ. It is not, however, the sole 

 or even the most important organ of respiration, since gaseous 

 exchange takes place over the whole surface of the larva. It is 

 concluded that in Apanteles and Microgaster the vesicle, when at 

 its maximum development, cannot be responsible for more than 

 about one-third of the total respiration. In other Braconids 

 (Orgilus) its respiratory function is less. The caudal vesicle found 

 in Apanteles, Microgaster, Microplitis, and some other Braconid 

 larvae has been much discussed by various investigators (vide 

 Tothill, 1922). It is evidently the everted proctodaeum which 

 becomes gradually withdrawn into the body during later growth 



