INSECTA 



427 



labium. Such a fusion characterizes the maxillipeds of certain Crus- 

 tacea. The primitive and generaHzed condition is, undoubtedly, that 

 which is found in insects which feed on soHd food, e.g. the Cockroach 

 or MachiHs. The mandible which is rarely jointed, represents the 

 toothed basal segment of an, originally, jointed limb, and corre- 

 sponds in form and function, to that of Crustacea, but never possesses 

 a palp (Fig. 301). Each first maxilla is articulated to the head by a 





Fig. 301. Mouth parts of Machilis (Petrobius) maritimiis. After Imms. 

 I, Mandible. 2, Maxilla. 3, Hypopharynx (li.) and superlinguae {sL). 

 4, Labium, c. cardo; g. galea; gl. glossa; /. lacinia; Ip. labium; m. post 

 mentum ; 7nx.p. maxillary palp ; pf. palpifer ; pg. paraglossa ; p?n. prementum ; 

 pgr. palpiger; s. stipes. 



basal segment, the cardo. The succeeding segment, the stipes, carries 

 an outer palp bearing sclerite, and distally, bears two lobes, inner 

 spiny lacinia, and outer hood-like galea. In the labium, the basal 

 plates corresponding to cardo and stipes of the two sides, are fused 

 to form the suhmentum and post mentum. The more distal prementum 

 bears a palp at either side and a number of lobes, typically four, between 



