1921] Crampton: Sclerites of the Head 81 
such as Bittacus (Fig. 85), Panorpa (Fig. 82), etc., before attempting to 
homologize the parts in the highly specialized order Diptera, instead of 
attempting to compare the Diptera directly with the lower orders such’ 
as the Orthoptera, etc., since the Neuroptera and Mecoptera men- 
tioned above furnish the key to the interpretation of the parts in the 
Diptera, and the evidence they offer is most convincing. Wesche, 
however, is probably responsible more than anyone else for the con- 
fusion of the interpretation of the parts of the trophi by recent Dipterists, 
and Peterson’s work is a great improvement over that of Wesche, 
Smith and others who have misinterpreted the structure of the mouth- 
parts in a most amazing fashion, due to the fact that they have ignored 
the intermediate forms between the lower orders and the higher ones 
in attempting to homologize the parts in Diptera. 
As I pointed out in a recent paper (Crampton, 1917) dealing with 
the head region of Neuroptera, Mecoptera, Diptera, etc., the labial 
palpi, “Ip,” of the Neuroptera such as Nemoptera (Fig. 86) tend to 
become approximated in the median line of the head (compare Fig. 86 
with the Neuropteron shown in Fig. 81) while the ligula ‘‘lg”’ tends to 
disappear. A further step is represented by the Mecoptercn shown in 
Fig. 85, in which the ligula “Ig” of Fig. 86 has completely disappeared, 
although the labial palpi, “Ip,” have retained their typical three- 
segmented condition, and the palpigers, “‘pgr,”’ are still partially distinct. 
In the Mecopteron shown in Fig. 82, the labial palpi, ‘‘Ip,’’ have been 
reduced to two segments, the basal one being quite thick and ‘‘fleshy,”’ 
while the terminal one is small and slender. The sclerites which I have 
interpreted as the palpigers, “‘pgr,”’ (although they may possibly rep- 
resent the basal segments of the labial palpi instead) tend to unite, 
and the mentum ‘‘mn”’ is a broad plate somewhat produced anteriorly. 
A further modification is shown in the Mecopteron depicted in Fig. 84, 
the labial palpi being reduced to the fleshly lobes, ‘‘Ip,’’ while the pal- 
pigers have united to form the region ‘‘pgr,”’ which is but indistinctly 
demarked from the mentum ‘‘mn” behind it. The labial palpi, ‘“‘Ip,”’ 
have even developed ‘pseudotrachez”’ like those occurring on the labial 
lobes of certain Diptera, in some of the Mecoptera; and the whole 
trend of development in the Mecoptera indicates the origin of the 
inherent tendencies which find opportunity for fuller expression in the 
Diptera. Thus in the Dipteron shown in Fig. 83, the labial palpi ‘‘lp”’ 
are fleshy lobes like those of certain Mecoptera,* and they have even 
retained traces of two segments in the Dipteron shown in Fig. 83, which 
in this respect is more primitive than the Mecopteron shown in Fig. 84. 
The palpigers, “‘pgr,” of Fig. 83 are also distinct, although they have 
completely united in the insect shown in Fig. 84, to form the region 
labeled “pgr.”” The narrow median structure labeled ‘‘mn”’ in Fig. 83, 
is clearly the mentum. When one compares the Diptera with the 
* Dr. Tillyard, to whom I have shown the accompanying figures, in discussing 
the interpretation of the mouthparts of the Diptera, informs me that he has come 
to the same conclusion, independently, in comparing the head structures of Diptera 
with those of the Mecoptera, thus giving additional weight to the correctness of 
the interpretation here offered. 
