512 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



form themselves. It is far from being so in the case of the cater- 

 pillars rendered immobile by Synagris, which lie quite inert in the 

 earthen cell and scarcely show any signs of remaining alive, beyond 

 slight movements of the mandibles and head. 



The egg is deposited beside them, and is not fixed to the wall of 

 the nest by a suspensory thread, although this thread still exists at- 

 tached to one end of the egg. The egg, furthermore, is not fixed to 

 the prey, as in the case of such predaceous wasps as Bembex, Oxy- 

 belus, Ammophila, Pompilus, etc. It is deposited in the bottom of the 

 cell, which is at the time empty, and the female watches for the 

 hatching in order to begin provisioning. This is, therefore, the habit 

 of social wasps. One of the wasps, Monedula punctata, has nearly 

 the same habit, according to Mr. Hudson (ex Bouvier, p. 26). This 

 wasp digs a hole, deposits its egg therein, and then closes the hole and 

 waits for the hatching of the young larva before undertaking the 

 provisioning. But, as Bouvier has remarked, this proceeding hardly 

 constitutes a marked advance in the evolution of instinct. The young 

 Bembex, at its birth, finds itself immured in an empty cell. It does 

 not find at its door the food that it needs after hatching. One can 

 understand, however, the protection of the egg which is assured in 

 this way against the attacks of the Tachina flies. The proceeding of 

 our Synagris is much more perfected. The wasp does not wall up 

 its cell after laying the egg. It remains there itself and guards the 

 egg — its head directed outward, thus preventing the access of para- 

 sites. On the other hand, it begins provisioning at such time as will 

 enable the young Larva, after hatching, to be certain to find its food. 

 The provisioning which then takes place regularly and in proportion 

 suitable to the size of the larva, permits the Synagris to watch the 

 growth of its young. This is certainly an important advance over the 

 primitive mode of rearing the young found among the solitary wasps. 

 The larva is not walled up in the cell, which is abundantly supplied 

 with caterpillars, until it has reached a period of active growth, 

 which guarantees, to a certain extent, a favorable termination of its 

 evolution. 



The usual mode of provisioning, in which the egg is abandoned to 

 itself in the midst of an abundant supply of caterpillars, is mani- 

 festly imperfect. It may happen that the prey which has been col- 

 lected at one time in a single locality may be already infested with 

 parasites. In this case, these caterpillars, which are in such a condi- 

 tion that they can offer little resistance, soon perish and decompose, 

 involving the death of the larva which they should serve as food. 

 It may happen also that their tissues having been partly devoured 

 by their parasites, the amount of food is insufficient for the complete 

 growth of the young wasp. This occurred, as we have seen, in the 

 case of at least one of the larva? of our Synagris calida. Such an 



