PSYCHE. 



THE SEGMENTATION OF THE INSECT HEAD. 



BY JUSTUS WATSON FOLSOM, CAMBRIDGE, MASS. 



The elucidation of the primitive 

 segments in arthropods is a most inter- 

 esting and difficult morphological 

 problem. The rule of Savigny — 

 emphasized by Huxley and others — 

 that arthropods are fundamentally con- 

 structed of successive rings, each of 

 which may bear but one pair of pri- 

 mary appendages, although now un- 

 doubted, has never been thoroughly 

 substantiated when applied to the 

 hexapod head. After 3'ears of argu- 

 ment, morphologists still disagree as to 

 the number of somites composing the 

 highly differentiated heads of insects. 

 Compare the latest text-books in respect 

 to the subject. Kolbe ('90) recognizes 

 five, as follows : 



1. Ursegment : Fiihler, Augen, Oberlippe. 



2. " Oberkiefer oder Mandibeln. 



3. " Untei'kiefer Oder Maxillen. 

 [4. " Zunge Oder Innenlippe.] 

 5. " Unterlippe. 



Sharp ('95) says, " Morphologists 

 are not yet agreed as to their number, 

 some thinking this is three while others 

 place it as high as seven : three or four 

 being, perhaps, the figures at present 

 most in favour, though Viallanes, who 

 has recently discussed the subject, con- 

 siders six, the number suggested by 



Huxley, as the most probable. Cho- 

 lodkovsky is of a similar opinion." 

 Packard ('98) gives six: 



St'g-i>ie?it. Appendages, etc. 



r. Ocellar (Protocerebral). Compound and simple eyes. 



2. Antennal (Deutocerebral). Antennae. 



3. Premandibular, or inter- Preniandibular append- 



calary (Tritocerebral). ages. 



a.. Mandibular. Mandibles. 



5. First Maxillary. First Maxillae. 



6. Second Maxillary. Second Maxillae, or Lab- 



ium. Post-gula, gula, 

 submentum, hypopha- 

 rj-nx, (lingua, ligula), 

 paraglossae, spinneret. 



Upon anatomical grounds, different 

 observers have recognized from one to 

 seven head segments. As mentioned 

 by Packard ('98), Burmeister found 

 only two ; Cams and Audouin three; 

 MacLeay and Newman four ; Straus- 

 Durckheim seven. Huxley ('77) said, 

 "It is hardly open to doubt that the 

 mandibles, the maxillae, and the labium, 

 answer to the mandibles and the two 

 pairs of maxillae of the crustacean 

 mouth. In this case, one pair of 

 antennary organs found in the latter is 

 wanting in insects, as in other air- 

 breathing arthropods, and the existence 

 of the corresponding somite cannot be 

 proved. But if it be supposed to be 

 present, though without any appendage, 

 and if the eyes be taken to represent 



