392 



PSYCHE. 



[August 1899 . 



the appendages of another somite, the 

 insect-head will contain six somites." 



Huxley's conclusions were the most 

 satisfactory that could be derived from 

 a study of the completed organs alone 

 and reduced^the problem to these ques- 

 tions : Do the^eyes represent a somite? 

 Is another antennal segment represented 

 in insects ?2 Do the labrum and hypo- 

 pharynx represent distinct segments? 



Authors began to realize the impossi- 

 bility of settling the problem upon 

 purely anatomical data and attacked it 

 from the embiyological side. Packard 

 ('71), followed by Graber ('79), found 

 four cephalic somites: antennal, man- 

 dibular, first and second maxillary. 

 Viallanes ('87), however, wrote the 

 most important contribution upon the 

 subject after studying the development 

 of the nervous system in insects and 

 decapod Crustacea, and summarized his 

 results as follows. 



" La tete de 1' Insecte est form^e par 

 six zoonites, trois sont pr^buccaux et 

 trois post-buccaux. Le premier zoonite 

 porte les yeux composes et les ocelles. 

 Le deuxi^me les antennes. Le trois- 

 i^me, qui est depourvu d' appendices, 

 porte le labre, pi^ce qui, pas plus chez 

 les Insectes que chez les crustac^s, ne 

 pent etre considdree comme le resultat 

 de la soudure de deux appendices. Le 

 quatrieme zoonite porte les mandibules, 

 le cinqui^me les mdchoires, le sixr^me 

 la 16vre inf^rieure." These conclusions 

 have been confirmed by Wheeler ('93), 

 Heymons ('95, '97) and others. 



Rudimentary intercalary, or preman- 

 dibular, appendages have been found 



in Anurida (Wheeler '93, Claypole 

 '98) and Campodea (Uzel '97), and 

 the last two authors have homologlzed 

 them with the crustacean second 

 antennae. I maj' add that rudimentary 

 chitinized intercalary appendages per- 

 sist in adults of Tomocerus, Orchesella 

 and other Collembola. 



Six cephalic somites are the most 

 that have been admitted upon embryo- 

 logical grounds — but 1 am convinced 

 that six are not adequate. To prove 

 this statement, I must give a prelimi- 

 nary summary of some recent studies 

 upon the anatomy and development of 

 apterygote mouth-parts. 



The hypopharynx in Collembola and 

 Thysanura consists of three parts: a 

 median ventral lingua and two dorso- 

 lateral suferlinguae., hitherto termed 

 " paraglossae," but quite distinct from 

 the labial structures with the same 

 name. In the embryo of Anurida 

 maritima, the superlinguae originate as 

 a pair of simple papillae between the 

 mandibles and first maxillae and slightly 

 nearer the median plane. The super- 

 lingual anlagen are ectodermal evagi- 

 nations containing intrusive mesoderm 

 and are histologically undistinguishable 

 from the anlagen of the remaining 

 appendages. The lingua appears as a 

 subsequent and quite independent 

 median evagination of the first maxil- 

 lary segment and becomes supported 

 by a pair of lateral chitinous stalks 

 which originate in superficial grooves 

 of the germ band. 



Soon after involution has occurred, 

 just seven pairs of cephalic ganglia are 



