I DASYGASTRES OSMIA 49 



thus made is stored with pollen and honey, and an egg is 

 deposited. Then a barrier has to be constructed to close this 

 chamber ; the material used for the barrier is the pith of the 

 stem, and the Insect cuts the material required for the purpose 

 from the walls of the second chamber; the excavation of the 

 second chamber is, in fact, made to furnish the material for clos- 

 ing up the first cell. In this way a chain of cells is constructed, 

 their number being sometimes as many as fifteen. The mode 

 in which the bees, when the transformations of the larvae and 

 pupae have been completed, escape from the chain of cells, has 

 been the subject of much discussion, and errors have arisen from 

 inference being allowed to take the place of observation. Thus 

 Dufour, who noted this same mode of construction and arrange- 

 ment in another Hymenopteron (Odynerus nidulator), perceived 

 that there was only one orifice of exit, and also that the Insect 

 that was placed at the greatest distance from this was the 

 one that, being the oldest of the series, might be expected to 

 be the first ready to emerge ; and as the other cocoons would 

 necessarily be in the way of its getting out, he concluded that 

 the egg that was last laid produced the first Insect ready for 

 emergence. Fabre tested this by some ingenious experiments, 

 and found that this was not the case, but that the Insects became 

 ready to leave their place of imprisonment without any reference 

 to the order in which the eggs were laid, and he further noticed 

 some very curious facts with reference to the mode of emergence 

 of Osmia tridentata. Each Insect, when it desires to leave the 

 bramble stem, tears open the cocoon in which it is enclosed, and also 

 bites through the barrier placed by the mother between it and 

 the Insect that is next it, and that separates it from the orifice 

 of exit. Of course, if it happen to be the outside one of the 

 series it can then escape at once ; but if it should be one farther 

 down in the Indian file it will not touch the cocoon beyond, but 

 waits xDatiently, possibly for days ; if it then still find itself con- 

 fined it endeavours to escape by squeezing past the cocoon that 

 intervenes between it and liberty, and by biting away the material 

 at the sides so as to enlarge the passage ; it may succeed in doing 

 this, and so get out, but if it fail to make a side passage it will 

 not touch the cocoons that are in its way. In the ordinary 

 course of events, supposing all to go well with the family, all 

 the cocoons produce their inmates in a state for emergence within 

 VOL. VI E 



