WHEELER— THE PARASITIC ACULEATA. 11 



nourished; and hence, if we regard Bojiibus and Psithyrus of St. Fargeau, 

 Aglae and Euglossa, Mclccta and Anthophora, or Sphccodcs and Halictus, 

 with reference to their general structure, they will be found most intimately 

 allied; whilst if, on the other hand, we regard such portion of their economy 

 is is connected with the formation and provisioning of their nests, it will be 

 requisite to place them in different divisions. If we observe, however, the 

 great variation existing among bees in this portion of their economy, it is 

 evident that this cannot be regarded as a normal or typical character and 

 that a distribution founded thereupon would necessarily be unnatural." 



The publication of the " Origin of Species " could not fail to 

 have its efifect on the students of bees. In the light of evolution 

 the parasitic species acquired a new meaning, for it was at once 

 apparent that their resemblance to their hosts might have a genetic 

 significance. One of the first to fall under the spell of the new 

 conception was Hermann Miiller (1871). He believed that the 

 genus PsifJiynis was of rather recent descent from its host genus 

 Bomhus, that Melecta and Crocisa were less recently descended 

 from Anthophora, and that the phylogenetic origin of Stelis, Cocli- 

 oxys, Epeolus and Nomada was still more remote, although the 

 derivation of Stelis and Ca^Iioxys from gastrilegid genera seemed 

 clear. He was guided to these conclusions by a study of the an- 

 tennae. Referring to a table of the genera of bees he says: "An 

 examination of this table shows that in all nonparasitic bees, with- 

 out exception, the males have a shorter scape but a longer flagel- 

 lum than the females, but that in some pronounced cuckoo-bees the 

 very reverse is the case." Smell not only guides the males to the 

 females, but also the parasites to their hosts and hence the olfac- 

 tory organs of the female parasites must be highly developed. " A 

 glance at the development of the male and female olfactory organs 

 of the cuckoo-bees clearly supports the conclusion that in the an- 

 tennae of the females the adaptations for working in the brood- 

 chambers have been lost pari passu with an increase in the olfactory 

 organs and that these developments correspond in degree to the 

 period of time at which the transition to a parasitic life took place." 

 I am not aware that any study of the antennae and their sense- 

 organs has since been undertaken with a view to testing the correct- 

 ness of Miiller's conclusions. Allusion has already been made to 

 Graenicher's discovery that the vision of the parasitic bees is an 

 important factor in locating the nests of the host. 



