THE SKELETON OF THE HEAD OF INSECTS. 
JOHN HENRY COMSTOCK anp CHUJIRO KOCHI. 
Tue skeleton of the head of an insect is composed of several 
sclerites more or less closely united, forming a capsule, which 
includes a portion of the viscera, and to which are articulated 
certain appendages. 
The early entomologists, among whom were Fabricius (1775), 
Illiger (1800, 1806), Kirby (1802, 1826), Savigny (1816), Straus- 
Durckheim (1828), Burmeister (1832), Newman (1834), and 
Newport (1839), laid the foundation of our knowledge of the 
structure of this skeleton; and it is remarkable, considering 
the extent of entomological literature, how little has been 
added in this particular field since the publication of the article 
* [Insecta " by the last-named writer. 
Although comparatively little progress has been made in the 
study of the sclerites of the head during the last sixty years, 
very much has been learned by the workers of to-day regarding . 
the development of this region of the body ; and the time has 
come when, using the known facts of embryology as a starting 
point, one can hope, by comparative anatomical studies, to gain 
a clearer idea of the structure of the skeleton of the head than 
has been set forth as yet. To do this has been the aim of the 
writers of this paper. 
THE AREAS OF THE EXTERNAL SKELETON, 
In descriptions of insects it is necessary to refer to the dif- 
ferent regions of the surface of the head. This has resulted in 
the establishment of a nomenclature, which, although based on 
the work of the early insect anatomists, is really of compara- 
tively little morphological value ; for but few of the primitive 
sclerites of the head have remained distinct, and some of them 
greatly overshadow others in their development. The result 
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