THE KANSAS UNIVERSITY 

 SCIENCE BULLETIN. 



Vol. VI II , No .2] J ULY, 1 9 1 3. [ vI\TiirNa 2. 



Segmentation of the Head of Insects. 



Plates I to IV. 

 BY RUBY C. HOSFORD. 



THE question of the segmentation of the head of insects 

 has been much discussed, with the result that different 

 observers have recognized from one to seven segments 

 therein. 



Savigny (1816) made a very important step toward the' 

 solution of the problem by suggesting that the movable ap- 

 pendages of the head were homodynamous with legs. Com- 

 parative anatomists, then, accepting this and seeing that each 

 segment in the body of an insect has only one pair of appen- 

 dages, have concluded that there are at least four segments in 

 the head : i. e., the antennal, the mandibular, the maxillary, and 

 the second maxillary or labial. They also suggest that since 

 the eyes in certain Crustacea are borne on movable stalks, they 

 may be the appendages of a fifth segment. 



From this point the embryologist carries on the study. He 

 has found that in the embryo there exist distinct segments, 

 each corresponding to a pair of mouth parts. It has also been 

 found that in some stages of development there are at least 

 three pairs of distinct ganglia which go to make up the sub- 

 cesophageal ganglion. Each of these pairs of ganglia corre- 

 sponds to a pair of mouth parts. 



Wheeler ('93) observed rudimentary intercalary or pre- 

 mandibular appendages, which others have homologized with 

 the crustacean second antennse. Folsom has found rudimen- 



Received for publication March 20, 1913. 



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