44 Mr. S. S. Saunders's Description of 



came forth. The remaining pupae, selected as aforesaid, having 

 perhaps experienced some injury, never attained the imago state. 



From the ample stock of larvae and briars remaining, I ex- 

 pected to have been able to obtain a considerable number of the 

 parasites ; but in this I was mistaken, the gestation of the latter 

 apparently rendering the Hylceus precocious,* for none of the 

 bees whose metamorphoses were deferred to a late period pro- 

 duced any parasites ; such transformations being, in some cases, 

 exceedingly protracted and irregular. I noticed the same result 

 on other occasions, those bees which produced parasites being 

 always observed in the imago state before others not parasitically 

 affected ; their appearance varying, according to the season, from 

 about the middle of May to the middle of June. 



The parasitic pupae — with the exception of one possibly over- 

 looked at first — always appeared contemporaneously with the 

 imago-bee (never sooner), whose contortions in wriggling itself 

 out of the pupa-envelope may not impossibly assist the parasite 

 in driving the prominent carinated apex of the male pupae, or the 

 subcuspidate cephalo- thorax of the female, through the abdomi- 

 nal folds. Jurine, however, on one occasion discovered no less 

 than six larvae entirely concealed within the abdomen of a fully- 

 developed Polistes ;f and Mr. Westwood, also, " in examining the 

 interior of the abdomen (of an Andrena imago), from between the 

 segments of which the heads of two Stylops larvat were exserted, 

 found a third larva similarly attached, but entirely hidden within 

 the abdomen of the bee." J It may therefore be assumed, as 

 Dr. Siebold appears to think, that the preliminary act of pro- 

 truding its head is performed by the parasite previously to entering 

 upon the inert pupa state, its anterior region becoming indurated 

 about that period, and subsequently (as Professor Peck, of Boston, 

 also observed) presenting a " rounder form ;" although, indeed, 

 it may be difficult to determine with precision when the one 

 condition terminates and the other commences ; the outer tegu- 

 ment not being discarded at the time, but the real pupa or nymph 

 remaining encased, and finally divesting itself of its slender pel- 

 licle within ; where, as I shall have occasion to explain, it may 

 continue for some time undisclosed in the imago form. The 

 rapidity however with which, in these parasites on Hylceus, this 



* A similar circumstance was noticed by Mr. Thwaites, in a species of An- 

 drena ; as mentioned in Westwood 's Introd. Mod. Classif. of Insects, vol. ii. 

 p. 300, note. [Just as the presence of the Btastophaga by caprification renders 

 the figs precociously ripe. — Trans. Ent. Soc. vol. ii. p. 214.] 



-f Mem. Acad. Turin, torn, xxiii. 



t Trans. Ent. Soc. vol. ii. p. 185, note. 



