THE CANADIAN ENTOMOLOGIST 49 



certain from the facts in the case that the ancestors of Phasiop- 

 teryx possessed a microtype egg. 



It is a general rule throughout the Muscoidea that those 

 groups with greatest fecundity comprise parasitic forms whose 

 host-habits afford their maggots the least favourable opportunity 

 for encountering the host. Conversely the opposite is the case. 

 The fecundity runs highest in the Masiceratidce and Hystriciidce, 

 leaf-ovipositing and leaf-larvipositing parasitic forms, the 

 latter exhibiting the extreme Thus we may conclude that 

 in these groups there occurs the highest maggot mortality. Those 

 forms which are parasitic in white grubs, wood-boring grubs, and 

 hosts in general which the maggot must seek out for itself with 

 limited chance of finding them also have a high fecundity. The 

 Myiophasiice, which are weevil-grub parasites, have a much lower 

 fecundity, and it is evident that their maggots usually reach the 

 host. Forms which deposit eggs or maggots on the host also have 

 a comparatively low fecundity, and those which inject the maggots 

 or eggs subcutaneously have a still lower fecundity. The typical 

 Sarcophagine flies, which are non-parsaitic in the strict sense, 

 show on the whole the lowest fecundity of all, due to the nature 

 of their larval food-substances on which the highly active m.aggots 

 are deposited and which is ordinarily bountiful for their needs. 



The Sarcophagine flies have perhaps developed maggots 

 in utero on account of the generally perishable nature of their lar- 

 val food-substances, combined with a fairly long incubation period 

 necessary to the development of the maggot. On the other hand 

 the muscine and calliphorine flies have not done so, on account of 

 a marked difference in the nature of their food-substances which 

 are in general less perishable, combined with an incubation period 

 sufficiently short to meet the conditions and requirements of ovi- 

 position. It may be here pointed out that the most generalized 

 type of cephalopharyngeal skeleton so far known in the Muscoidea 

 is that exhibited in the first-stage maggots of the Sarcophagine 

 flies and their allies. Evidently the sclerites have here remained 

 almost unspecialized, being unreduced and freely articulated, as 

 best fitted for their larval life-habit. 



Returning again to taxonomic considerations, it is necessary 

 to point out more fully that however well the family types al- 



