ANURIDA. 371 



The maxillulae* (figs. 11 and 14) are intercalated 

 between the mandibles and the first maxillse. They are 

 situated immediately dorsad of the lingua, to which they 

 are closely applied. In form the maxillulse are broad 

 and plate-like, but are feebly chitinised and relatively 

 delicate structures. Along their anterior borders they 

 are finely serrated, and they each bear a tooth-like 

 projection at their outer angles. Unlike the first 

 maxillae, at no stage in their development do the 

 maxillulse exhibit any indications of a differentiation 

 into a galea and lacinia, neither are there any traces of 

 palpi. 



The lingua or tongue is a median unpaired structure, 

 and is moderately strongly chitinised (figs. 11 and 14). 

 It has a paired appearance owing to being lobed 

 anteriorly and in being grooved dorsally down the middle 

 line. Posteriorly, the lingua rests on two strong 

 chitinous props, which are termed the lingual stalks 

 (ling. st.). The latter structures are not, sensu stricto, parts 

 of the tongue ; they are developed as longitudinal thicken- 



* Most writers on the Collembola have referred to these organs 

 as paraglossse. The latter name, however, is undesirable since it 

 renders them liable to conf usion with parts bearing the same name 

 in the second maxillae of the Pterygota. Hansen (Zool. Anz., 1893) 

 was the first to recognise that they represented a complete and separ- 

 ate pair of gnathites and he termed them maxillulce. Seven years 

 later the embryological work of Folsom (10) definitely established the 

 truth of Hansen's conclusions. On account, however, of their 

 intimate relations with the lingua, Folsom named them superlingucB. 

 In the generalized Collembolan Isotoma palustris Carpenter has 

 recently shown (Proc. Boy. Irish Acad., 1903, vol. xxiv. ser. B. p. 325) 

 that the maxillulse are of a very primitive nature, each being sub- 

 divided into a galea and lacinia which have become lost in Amcrida. 

 Among the Thysanura the maxillulse are likewise differentiated into 

 a galea and lacinia, and a palp is present in addition. In the Pterygota 

 these gnathites have, as yet, been very little studied and they appear 

 to be either greatly reduced and very intimately associated with the 

 lingua or tongue (Orthoptera and Plectoptera) or atrophied altogether. 

 In the earwig-like genus Hemimerus the maxilluloe appear to approxi- 

 mate to the apterygote condition very closely (Hansen, Ent. Tidskr., 

 1894, p. 65). Folsom (10) regards the " hypopharynx " of the 

 Pterygota as being a composite structure formed by a fusion of the 

 maxillulse with the tongue. 



