PROC. ENT. SOC. WASH., VOL. 24, NO. 4, APR., 1922 89 



by Dr. Villeneuve as the gratiosa variety, it is not now possible 

 to say which of these two forms really corresponds to the variety 

 described by Brauer and von Bergenstamm, especially since 

 according to these two" authors (Denks. Akad. Wien. I. VII I, 

 330, 1891), both forms are blue-grey or grey-black species. 

 The adults corresponding to the three forms of larvae may be 

 separated somewhat as follows: 



Pollen of head and body yellowish senilis (t\ -picalj 



Pollen of head and both' bluish. 



Three rather ill defined anil broad post-sutural thoracic vittae 



senilis var. gratiosa (B. B.?) 

 Five well defined and narrow post-sutural thoracic vittae 



senilis var. "c. " 



However, as I possess but one specimen of the variety "c' : 

 and but three of the form provisionally called gratiosa, the value 

 of these distinctions, which in some species of Tachinids would 

 come well within the limits of specific variation, remains some- 

 what doubtful For this reason, in spite of the fact that the 

 differences between the primary larvae are sufficiently well 

 defined and apparently constant, it does not appear advisable 

 to create new specific or varietal names to cover any of the three 

 types of senilis , especially since the synonymy of this species is 

 already fairly extensive. To give these forms definite system- 

 atic status as species or even as varieties will not increase the 

 value of the differences between them nor will it make them any 

 easier to separate in the adult stage than they now are 



The case considered in this paper, of a species presenting in 

 the larval condition several morphologically distinct forms- 

 associated perhaps with different larval environments but 

 in the adult condition morphologically homogeneous or almost 

 so, belongs to a group of phenomena studied in a series of papers 

 by the eminent biologist Alfred Giard, and grouped by him 

 under the general techical term of pcecilogony (Giard, Oeuvres 

 Diverses, I Biologie, nos XLI-XLVI). 



The phenomenon of pcjecilogony if it really exists is not one 

 which either the systematician or the practical entomologist 

 can afford to neglect. If in a given "species" there exist races 

 or varieties almost or quite inseparable in the adult, which are 

 nevertheless separated in the larval stage by distinct and con- 

 stant differences, it follows that between these races there may 

 exist fundamental or constitutional differences which the prac- 

 tical worker is obliged to take into account. To make this 

 clear it will be sufficient to consider briefly the case of the para- 

 site studied in this paper. This species is in certain regions 

 of FAirope an important parasite of the Corn Borer ami an effort 

 is therefore being made by the I'nited States Bureau of Knto- 

 mology to introduce it into the North American areas invaded 



