276 BenJaAmMin. P. YounG 
This suture was found in species of all the families studied among the 
Calyptratae and the Acalyptratae, but in only one family outside of these 
two groups, in Myopa vesiculosa (Plate XX, 36) of the family Conopidae. 
Closely associated with the appearance of this suture is a tendency 
toward the coalescence of the first two abdominal tergites. This tend- 
ency toward fusion occurs in all the families of the Acalyptratae with the 
exception of the Scatophagidae (Plate X XV, 54), the Heteroneuridae (Plate 
XXV, 55), and the Helomyzidae (Plate X XV, 56); and in all the families 
of the Calyptratae with the exception of the Oestridae (Plate XXI, 
37). Aside from the families of these two groups it occurs only in the 
Conopidae (Plate XX, 36), the Pipunculidae (Plate XX, 34), the 
Platypezidae (Plate XIX, 33), and the Lonchopteridae (Plate XIX, 31). 
But at least five different stages in the development of this tendency can 
be pointed out if there are included the families showing both the adven- 
titious suture and a complete suture between the first and second tergites, 
as the Oestridae (Plate XXI, 37), the Scatophagidae (Plate XXV, 
54), the Heteroneuridae (Plate XXV, 55), and the Helomyzidae (Plate 
XXV, 56). The adventitious suture and only the dorsal part of the suture 
dividing the two tergites are found in the Conopidae (Plate XX, 36), 
the Sarcophagidae (Plate XXII, 40), the Sciomyzidae (Plate XXVI, 58), 
the Piophilidae (Plate XXVIII, 65), and the Geomyzidae (Plate XXX, 
71). Further, the adventitious suture and only the ventral part of the 
suture dividing the first and second tergites are found in the Borboridae 
. (Plate XXVI, 57), the Sapromyzidae (Plate XX VI, 59), the Ortalidae 
(Plate X XVIT, 60), the Sepsidae (Plate XX VIII, 64), the Ephydridae (Plate 
XXIX, 68), the Oscinidae (Plate XXX, 69), and the Drosophilidae 
(Plate XXX, 70). The next stage would be represented by families 
showing the adventitious suture alone, in a few cases the suture between 
the tergites being represented by a semblance of membrane, as in the 
Tachinidae (Plate X XI, 38), the Dexiidae (Plate X XI, 39), the Muscidae 
(Plate XXII, 41), the Anthomyiidae (Plate X XII, 42), the Rhopalomeridae 
(Plate X XVII, 61), the Trypetidae (Plate X XVII, 62), the Micropezidae 
(Plate XXVIII, 63), the Psilidae (Plate X XIX, 66), the Diopsidae (Plate 
XXIX, 67), and the Agromyzidae (Plate XXXI, 72). Finally, in some 
families no marked evidence of either suture was to be found, as in the 
Lonchopteridae (Plate XIX, 31), the Platypezidae (Plate XIX, 33), and 
the Pipunculidae (Plate XX, 34). Among the species of anthomyids 
