98 Annals Entomological Society of America  [Vol. XIV, 
A study of the embryological development of the head of an 
insect and a comparison with the head region of the Crustacea 
(which are like the ancestors of insects) would indicate that 
six primitive segments enter into the composition of the head 
of an insect. The protocephalon, antennal, intercalary, man- 
dibular, first maxillary, and second maxillary (labial) segments 
of an insect’s head correspond to the protocephalon, antennular, 
antennal, mandibular, first maxillary, and second maxillary 
segments, respectively, in a crustacean’s head. The so-called 
‘“‘superlingue’’ of insects are homologous with the paragnaths, 
not with the ‘‘maxillule’’ (first maxille) of Crustacea. The 
mandible of an insect represents only one (the basal) segment 
of a crustacean’s limb, while the body of the maxilla of an 
insect is composed of several segments of such a limb, so that 
the parts of an insect’s maxilla are not represented in the 
mandible. 
In conjunction with other structures of the body, the head 
region of insects furnishes indications of a relationship to the 
Crustacea on the one side, and to the Symphyla on the other. 
Machilis among the Apterygota, and the ephemerids among 
the Pterygota have retained a number of features suggestive 
of affinities with the Crustacea, and the head region of Machilis 
would indicate that it is an extremely ancient type related to 
such forms as Lepisma Nicoletia, etc. (and also to Japyx and 
Cam podea) on the one hand, and to the Collembola on the other. 
The head of Machilis, Lepisma and WNicoletia among the 
Apterygota have more suggestions of crustacean affinities, 
while the head of Japyx and: Campodea is very like that of 
Scolopendrella and other Symphyla-like forms. 
Lepisma offers a connecting link between Machilis (which 
leads to the crustacean forms) and the lower winged insects 
such as the Plecoptera, ephemerids, etc., and the head of 
immature Plecoptera approach as closely as any type, to that of 
Lepisma. The head of an immature Plecopteron on the other 
hand, is extremely similar to that of Arixenia among the 
Dermaptera. The head structures of the Dermaptera (and the 
Embiide also) in turn lead to the type found in Coleoptera, 
particularly in the structure of the maxilla. As we trace the 
head types from the Coleoptera upward, the Neuroptera appear 
to be the next of kin, since the head structures of larval Coleop- 
tera and Neuroptera are astonishingly alike. The Neuroptera 
