OX THE STRUCTURE OF BiAXlLLUL.l" IX INSECTS. 429 



On the Structure and Occurrence of Maxillulse in the Orders of. Insects. 

 By Alwex M. Evans, M.Sc. (Manch.), Depfc. of Medical Entomology, 

 Liverpool School of Tropical Medicine. (Communicated by Dr. A. D. 

 Immb, F.L.S.) 



(Plate 31, and 17 Text-figures.) 

 [Read 5th June, 1910.] 



CONTENTS. 



Introduction, p. 429; Apterygota, p. .430; Dermapteia, p. 433; Orthoptera, p. 434; 

 Ephemeridse, p. 435 ; Perlaria, p. 436 ; Psocidre and Mallophaga, p. 437 ; Neuroptera, p. 439 ; 

 Coleoptera, p. 442 ; Lepidoptera, p. 445 ; Triehoptera, p. 447 ; Ilynieuoptera Tenthredinese, 

 p. 448; Diptera, p. 451 ; Summary of Conclusions, p. 452 ; Bibliography, p. 454; Explana- 

 tion of l J late 31, p. 456. 



Introduction. 



A quarter of a century ago Hansen (1893) originated the theory that the 

 pair of appendages associated with the hypopharnyx of Maeliilis and other 

 Apterygota is homologous with the maxillula? of Crustacea (21) *. The 

 theory has since been raised to the status of an established fact, chiefly 

 by the embryological researches of Folsom. In the paper in which his 

 results are recorded, Folsom (17. p. 116) stated that "The superlingiue 

 (maxillulaj) should hereafter be recognised as morphologically important 

 structures, and be searched for in even the most specialised haustellate 

 orders " 



Since this forecast was made its value has been proved by reasearches on 

 the constitution of the hypopharynx in Coleoptera and Lepidoptera. In the 

 larvae of certain genera of these orders the presence of structures of 

 undoubtedly maxillular nature has been demonstrated. 



The present paper is a record of investigations whose object has been to 

 determine as far as possible the occurrence of structures comparable with 

 maxillulaa in the various orders of insects. In the haustellate orders only 

 the mandibulate larvae are considered. The Hemiptera, Mecaptera, and 

 Thysanoptera are not dealt with. Some attempt is made to compare the 

 form of maxillulse characteristic of different orders and, where enough 

 material has been available, to study the distribution and variation of these 

 structures within the order. 



I wish to express my gratitude to Professor S. J. Hickson, F.R.S., who 



* My attention has recently been called to the fact that Lubbcck in his monograph of 

 the Thysanura and Collembola recognises the maxillulse as appendicular structures, referring 

 to them as " a second pair of maxillse." 



