ySo THE AMERICAN NATURALIST. [Vol. XXXVIII. 



appendages of the first somite are sessile and those of the sec- 

 ond or third undeveloped." 



I shall have occasion to revert to this paper of Huxley's, for, 

 as we shall see, he devoted considerable attention to a consider- 

 ation of the development of the head, and brought out some 

 facts of prime importance. 



Packard ('66), believed that the insectean head was composed 

 of seven segments. In 1870, in the second edition of the Guide 

 to t/ic St7idv of Insects, he gives a table of these segments and 

 their appendages. He believed the segments to be a first ocel- 

 lary, second oce/laiy, opt/ia/mic, antennary, mandibular, first 

 maxillary, and a second maxillary or labial. In addition to these 

 seven he includes a hypothetical first segment whose tergal parts 

 give rise to the .labrum, epipharynx, and clypeus.^ Thus at this 

 time he regarded the insectean head as composed of eight prim- 

 ary segments. 



In 1 87 1, however, Packard presents evidence to show that 

 the ocelli and the compound eyes do not represent appendages. 

 "Accordingly," he says, "we seem forced to the belief that the 

 head of the hexapodous insect consists of but four segments, i. e., 

 the second maxillary, the first maxillary, and mandibular seg- 

 ments behind the mouth opening and the antennary, or first and 

 preoral segment situated in front of the mouth." This view he 

 reiterates in 1883. In 1898 he tabulates six segments. 



One of the most recent workers to approach this subject is 

 Janet ('99). leasing his conclusions largely on a study of the 

 musc-iihuurc of the adult Vcspa, this worker states that the 

 so-called primary head segment -- the protocerebral segment of 

 authors — is in reality composed of four segments and that there- 

 fore the head of an insect is made u]) of not less than nine seg- 

 ments, all ()f vvhich were primitively postoral. According to 



2° Le somite lesophagien 



3° Le somite clypco-pharyngien 



ou somite proto-stomodseal 

 ou somite deuto-stomodseal 

 ou somite trito-stomoda^al 



