Insects. 6909 



great saw-fly operates upon the top of its cocoon. On a close 

 inspection of the interior of the cell after the insect had quitted it, 

 1 could detect the presence of nothing to indicate that the parasite 

 was not the original, or had not been the sole, tenant. This fact, 

 coupled with the pointed form of the covering, led me to think it not 

 improbable that an analogy might exist between the habits of this 

 parasite and those of the cuckoo, — that as the e^,g of the latter is 

 palmed off upon the unsophisticated, unsuspecting wagtail as one of 

 her own, so might those of the former be palmed off upon the nursing 

 wasps as genuine eggs of their own species ; and that the larvae might 

 be nursed, tended, fed and brought to maturity by the attendant 

 wasps, just as the dupe of a wagtail brings to maturity the young 

 cuckoo. 



Unaware that this idea had been entertained by any one previously, 

 I mentioned it in a note to Mr. Douglas, who informed me that 

 Latreille had inferred as much from observations he had made. Had 

 my attention been directed to the subject at the time I first obtained 

 possession of this nest, I should doubtless have been enabled to prove 

 the soundness or unsoundness of the above conjecture ; as it is, the 

 question must remain an open one till another year, when I hope to 

 have an opportunity of deciding it. 



The parasites betake themselves to flight, leaving the nest in all 

 haste the moment they have freed themselves from the cells, as 

 though afraid to prolong their stay among those upon whom they 

 have so long and so successfully imposed, now that they have thrown 

 off the cheat and appeared in their true colours. How the parent 

 insects contrive to enter the nest with impunity, and deposit their 

 eggs without molestation (always provided they do enter it for that 

 purpose), is a point upon which renewed observations, made at an 

 earlier period in the season, may possibly throw some light. It may 

 probably be found that they do not actually enter the nest, but con- 

 tent themselves, like Sitaris, with depositing their eggs somewhere in 

 the immediate vicinity, trusting, as Sitaris does, to the exertions of 

 the larvae to gain access to the cells in the best way they can ; and 

 when the latter have done this there are two courses open to them, 

 one of which it is clear they must pursue : they can either select a 

 cell containing an egg, which they can first coolly despatch for 

 breakfast, as it appears the larvae of Sitaris do, and then pass them- 

 selves off as wasp-larvae ; or they can look out for one containing a 

 larva, into whose body they can enter, and upon which they can feed 

 till their change comes, as the Ichneumonidae do upon the bodies of 



