1921] Crampton: Sclerites of the Head 67 
Despite the fact that a large number of papers have been 
published dealing with the head structures of insects, the 
boundaries of the various head sclerites have not in many 
instances been clearly defined; and in the higher insects, such 
as the Diptera, the parts of the labium, for example, have not 
been interpreted correctly in the recent papers dealing with the 
subject. Even the most basic and fundamental features of 
the composition of an insect’s head are not understood and 
interpreted aright in most of the recent textbooks and articles 
which treat of this phase of the subject, and it is quite apparent 
that there is a decided need of a thorough-going review of the 
whole subject of the head region of insects and the interpretation 
of its parts. Thus, for example, everyone who has recently 
discussed the superlinguz or ‘‘paraglosse’’ of insects (i. e., 
the lobes on either side of the hypopharynx) homologizes them 
with the maxillule (first maxilla), instead of with the paragnaths 
of Crustacea, as should be done. (See references to origin of 
superlingue, mandibles, maxille, etc., in bibliography). In 
most textbooks one sees the incorrect statement that the 
maxillary galea and palpus represent the two forks of a biramous 
limb, instead of the correct interpretation of the palpus as the 
distal segments of a limb (endopodite) in which the second or 
stipes segment, and the third or palpifer segment have developed 
endites or lobe-like processes forming the galea and lacinia. 
The statement that the parts of the maxilla are represented 
in the mandible, which one encounters in many publications, 
is wholly incorrect, since the mandible represents but a single 
segment of a limb, while the maxilla is composed of more 
than one segment of such a limb. The statement that the 
- head of an insect is composed of seven segments, instead of but 
six (as embryology has long ‘shown to be the case) is another 
instance of the many glaring inaccuracies one encounters on 
every hand in reading the literature dealing with the head region 
of insects; but since these matters have been discussed more at 
length in a series of articles dealing with each phase of the 
subject in detail, the following discussion is restricted to an 
attempt to determine the boundaries of the sclerites of the 
head in insects in general, and to interpret the structure of the 
parts of the head of higher insects in terms of those of the lower 
forms by using for study, as far as possible, the intermediate 
types serving to connect the higher with the lower insects. 
