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regular dehiscence of an apical cap. The pupa itself, as it ap- 

 proaches maturity, is more or less visible through the shell. It 

 appears to me of a decidedly Coleopterous type, and when the 

 mature insect emerges the pupal skin is shed as the most deli- 

 cate of pellicles. 



SOME RELATIONS OF PARASITE AND HOST. 



In the case of Xenos parasitic on wasps of the genus Folistes, 

 Hubbard noted the marked hostility of the host towards the 

 parasite. Brues did not observe this with his specimens, and 

 suggests that this was due to the fact that no females of the 

 Xcnos were present in the wasps that he studied, and conse- 

 quently that the males of the parasite did not approach these 

 for the purpose of pairing. This is very probably the true ex- 

 planation of the difference in the wasps' behaviour in the two 

 cases, in confirmation of which one may cite the old and often 

 quoted observation of J. C. Dale: "Puiting two bees (Aiidrciia 

 labialis) under a glass in the sun two Stylops were produced: the 

 bees seemed uneasy and went up towards them, but evidently 

 with caution, as if to fight; and moving their antennae towards 

 them, retreated. I once thought the bee attempted to seize it ; 

 but the oddest thing was to see the Stylops get on the body of 

 the bee and ride about, the latter using every effort to throw 

 his rider." This certainly seems to point to the conclusion ar- 

 rived at by Brues, the Andrcna in question probably bearing a 

 female specimen of the parasite. In the case of leaf-hoppers, 

 we did not notice any sign of disturbance on the part of the 

 host at the presence of the male parasites, nor did we ever see 

 copulation take place, though we often had many male and 

 female Elcnchiis in the same jar. It will probably prove that 

 the remarkable mandibles of many male Stylopids- are for the 

 purpose of 'holding on to the host during the pairinlg of the 

 sexes. In general it would appear that these organs are less 

 remarkable in the parasites that attack leaf-hoppers, than in 

 those that occur in bees and wasps, in fact in some of the former 

 class they are small and of very simple form. 



In the case of Polistcs there is, according to Brues, a well- 

 rrarked tendency for all the parasites in one wasp to develoj? 

 the same sex. This is also notably the case with some of the 

 Stylopids affecting the Fossorial Hymenoptera, but with those 

 attacking leaf-hoppers it is often quite otherwise, and it is of 

 the commonest occurrence to find male and female parasites in 

 the same individual hopper. 



