We know that the social wasps differ from the honeybee in that their large cells are reserved for the true females, while the little ones are intended for the rearing of the males and of the sterile females called workers.
But it appears from the beautiful observations of Marchai on the German wasp: first, that the queen lays "in a continuous manner until the end of July or the beginning of August" worker eggs in the little cells ; secondly, that then the big cells are built which ' ' thus give the choice to the queen between the two distinct kinds of cell"; thirdly, that afterward the large cells receive exclusively female eggs, while the little ones are provided by chance with the eggs of males or workers.
Marchai very happily explains these facts by a variation in the contractility of the seminal receptacle by a kind of muscular fatigue already suggested by Dadant for the bees. After the long uninterrupted laying of workers, which lasts until the beginning of August, "the reflex which brings the contraction of the seminal receptacle to the moment of the laying of each egg is no longer produced with the same regularity and . . . then the eggs can be laid without being fertilized. Therefore," says Marchai, "the almost sudden appearance of males is due to the relatively inert condition of the receptacle. Thus the queen does not lay male and female eggs at volition, but a moment arrives when her laying perforce contains males because of the relative inertia of her receptacle, and her active role consists in distributing the eggs according to the sex," in a very precise manner in the large cells which receive only the eggs of fertilizable females or by chance in the little ones where are ordinarily placed the worker eggs or the male eggs.
Why does the queen place fertilized eggs exclusively in the large cells! One cannot suggest mechanical hypotheses, for it is hardly probable that the large size of these cells causes the closing of the seminal receptacle with the bees and its opening with the wasps. As we have done with the bees, Marchai attributes the reflex opening to a psychical phenomenon. The large cells, he says, "have the faculty of stimulating the queen, who seems in certain cases to have a marked preference for them. It must be admitted that upon these large cells she concentrates all her energy and that on this account she will lay in them only fertilized eggs." Here, as with the bees, the laying of male eggs seems to be the manifestation of an annual rhythm, but in this case it does not reach the same precision. With the bees, in fact, the laying of these eggs seems to be continuous during a short period in the spring-time, while with the wasps it begins in the middle of summer, to continue during the autumn, alternating with the laying of worker eggs. This is a lower stage in the division of sexes.