THE EXO-SKELETON OF THE PROBOSCIS. 131 



which the palpi are always developed.' He regards the palpi 

 of the Diptera as labial, and not as maxillary, a conclusion 

 which appears to me to be unwarranted. They are, without the 

 slightest doubt, maxillary palpi. 



If the proboscis of the Diptera represents the first, and not 

 the second, pair of maxillae, the four-jointed sheath of the 

 Hemiptera must unquestionably have the same morphological 

 value. 



I have repeatedly examined the mouth organs of the larger 

 Cicadae, and the conclusion at which I have arrived is, that the 

 sheath exhibits no indications of its morphological identity with 

 either the labium or the maxillae which would enable one to 

 judge whether it represents the one or the other ; but there 

 is no evidence that both pairs of maxillae are developed, or that 

 either pair of setae should be identified as representatives of the 

 first pair. 



Just as nearly everyone has accepted the statement that the 

 greater part of the proboscis of the Diptera represents the 

 labium, so they have accepted the statement that the sheath 

 of the lancets in the Hemiptera is a modified labium ; yet 

 this view which Savigny initiated depends mainly upon the 

 supposed identification of the second pair of setae with the 

 maxillae. Against this identification, I would observe, there 

 is no evidence that a seta can be homologous with a maxilla, 

 and the manner in which these setae are connected with the 

 head shows at once that they are not the maxillae. Latreille 

 identified them with the terminal lobes of the maxillae, a much 

 more correct view of their homology.* 



Before entering upon a detailed examination of the proboscis 

 with a view to elucidate its real nature from a morphological 

 point of view, it is essential to acquire a definite idea of the 

 nature and structure of the labium and maxillae in insects. 



The Labium. Erichson [52] discusses the mouth parts of 

 insects ; in especial relation to the structure of the labium, or 

 lower lip, he says : 



' The third pair of jaws, in the Insecta, form a considerable 



* Cuvier, ' Regne Animal,' Nouvelle edit., Svo, Paris, 1829, torn, v., p. 190. 



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