Bramble-bees and Others 



which we introduce on the slightest provoca- 

 tion as a convenient explanation of that which 

 may transcend our explanatory powers. 



My next test is made with a string of live 

 cocoons. Of course, I cannot take all these 

 from the same species, for then the experi- 

 ment would not differ from the one which we 

 have already witnessed; I take them from two 

 different species which leave their bramble- 

 stem at separate periods. Moreover, these 

 cocoons must have nearly the same diameter 

 to allow of their being stacked in a tube with- 

 out leaving an empty space between them and 

 the wall. The two species adopted are Sole- 

 n'uis vagus, who quits the bramble at the end 

 of June, and Osm'ia detrita, who comes a lit- 

 tle earlier, in the first fortnight of the same 

 month. I therefore alternate Osmia-cocoons 

 and Solenius-cocoons, with the latter at the 

 top of the series, either In glass tubes or be- 

 tween two bramble-troughs joined into a cylin- 

 der. 



The result of this promiscuity is strik- 

 ing. The Osmix', who mature earlier, 

 emerge; and the Solenius-cocoons, as well as 

 their inhabitants, who by this time have 

 reached the perfect stage, are reduced to 



33 



