ATTACHMENT OF THE ABDOMEN TO THE THORAX IN DIPTERA 277 
studied, two of these stages were represented, eight species showing the 
adventitious suture and the ventral part of the suture separating the first 
_and second tergites, and four species showing only the adventitious suture. 
In drawing conclusions regarding any uniformities existing among 
Diptera in respect to the location of abdominal spiracles, perhaps it 
would be best to disregard the first and those beyond the fifth segment, 
and consider only the second, third, fourth, and fifth segments. The 
integument in which the first abdominal spiracle is located is the most 
subject to change, as it is just at the point of attachment of the abdo- 
men to the thorax. As there is a necessity for flexibility at this point, the 
body wall is usually membranous, and as a result the first abdominal 
spiracle is, with few exceptions, as in the cyrtid (Plate XVI, 23), the 
lonchopterid (Plate XIX, 31), the tachinid (Plate X XI, 38), the dexiid 
(Plate X XI, 39), and three species of anthomyids (Plates XXII, 42, and 
XXIII, 45 and 48), found in membrane. Beyond the fifth segment, the 
spiracles are so affected by the forces producing the modification of the 
segments into the genitalia that these too are unreliable. But in consider- 
ing the second, third, fourth, and fifth spiracles in regard to location in 
membrane or chitin, some uniformities are seen. All four of these spir- 
acles in each family of the Calyptratae except the Oestridae, in which 
all are in the membrane, are found in chitin. Among the Acalyptratae, 
all four spiracles in the Scatophagidae and the Ephydridae, and the third, 
fourth, and fifth in the Oscinidae, are found in chitin. All other represent- 
atives of families have these spiracles in membrane. Aside from these 
two groups, only scattered cases are found in which these spiracles are 
surrounded by chitin. In the Cyrtidae, all four are in chitin; in the 
Lonchopteridae and the Platypezidae, only the third, fourth, and fifth 
are in chitin. 
The pleuro-trochantin (ptn’) of the metathorax appears as a chitinized 
sclerite in all the Cyclorrhapha, with the possible exception of the Oestridae 
(Plate X XI, 37), the Tachinidae (Plate X XI, 38), and the Pipunculidae 
(Plate XX, 34). Among the Brachycera there seem to be two families 
showing true chitin in this sclerite, the Asilidae (Plate X VIII, 28) and the 
Lonchopteridae (Plate XIX, 31). This sclerite appears as membrane or 
as questionable chitin, if at all, in all other families. 
In a few families it was rather difficult to separate the epimeron of the 
metathorax from the sclerites of the first abdominal segment. ‘These 
