66 KANSAS UNIVERSITY SCIENCE BULLETIN. 



tary chitinized intercalary appendages in adults of Tomocerus, 

 Orchesella, and other Collembola. 



Folsom in his study of the embryo of Anurida found seven 

 pairs of primary ganglia, the extra one being the fifth, between 

 those of the mandibular and maxillary segments. This is called 

 the superlingual segment. According, then, to the conclusions 

 set forth from the study of comparative anatomy and embry- 

 ology, the insect head is composed of seven segments: the 

 anten^ial, the mandibular, the maxillary, the second maxillary 

 or labial, the premandibular or intercalary, the ocular, and the 

 superlingual. 



The order of arrangement of these segments may be de- 

 termined by the position of the primitive ganglia that inner- 

 vates them. 



The supracesophageal ganglion, or the brain, is composed of 

 three pairs of primary ganglia : the protocerebrum innei-vates 

 the compound eyes and the ocelli or the ocular segment; the 

 deutocerebrum, the antennje or antennal segment; and the 

 tritocerebrum, the labrum or premandibular segment. The 

 .suboesophageal ganglion is composed of four pairs of primary 

 ganglia : the first innervates the mandibles or mandibular seg- 

 ment; the second, the superlingute or superlingual segment; 

 the third, the maxillae or maxillary segment; and the fourth, 

 the labium or second maxillary segment. 



We have, then, the following order : 



1. — Ocular. 

 2. — Antennal. 

 3. — Intercalary. 

 4. — Mandibular. 

 5. — Superlingual. 

 6. — Maxillary. 

 7. — Labial. 



Having now decided that there are seven segments united 

 to form the head capsule of insects, we wish to determine what 

 sclerites belong to the different segments. Using the work of 

 Gomstock and Kochi as a working outline, I have endeavored 

 by a series of comparisons to form for myself an opinion on at 

 least some of the following points : 



Areas of the external skeleton of the head ; the structure of 

 a typical segment; and the sclerites belonging to each head 

 segment. 



