THE EXO-SKELETOX OF THE PROBOSCIS. 129 



bristles. The hypopharynx* and the epipharynx are also con- 

 verted into bristles, and the labrum is a bristle on a larger 

 scale, which covers all the others.' 



Savigny produced no evidence in support of these statements, 

 yet they have been almost universally accepted ; neither, so far 

 as I know, has anyone adduced any in the seventy years which 

 have elapsed since the publication of his work. Savigny did 

 prove, however, and proved in a very masterly manner, that 

 the paired mouth organs of insects, the mandibles, maxillae 

 and lower lip, or labium, are homologues of the thoracic legs, 

 and that in the highly modified suctorial mouth of the Lepi- 

 doptera there is a great development of the maxillae, with a 

 corresponding reduction in the magnitude and complexity of 

 the labium and mandibles. 



In the Diptera the only reason for regarding the terminal 

 portion of the proboscis as a modified labium or lower lip is 

 its position, and this is no evidence of its nature from a mor- 

 phological point of view. 



The labium of an insect is not merely a lower lip ; it is 

 something more. It is a lower lip formed by the union of the 

 second pair of maxillae. 



As we ascend from the less to the more highly modified 

 Arthropoda, there is a tendency to the reduction of the number 

 of post-oral somites developed in the head. Amongst the 

 Crustacea the number of cephalo-thoracic metameres is in 

 excess of that in insects. The three pairs of ventral appen- 

 dages in Gammarus, which follow the mandibles, will be seen 

 to be all alike, except that the third pair are united to form a 

 lower lip. In the most generalised Insecta the second pair are 

 united, and there is no third pair. In the highly modified 

 Lepidopterous type the second pair of maxillae are rudimentary, 

 and the first pair form the large suctorial apparatus, whilst the 

 mandibles are rudimentary or absent. 



Before I undertook the investigation of the manner in which 



* The statement made by me on page 44, ' The ligula has no relation to 

 the hypopharynx of Savigny,' should have been, The ligula is not a Jiypo- 

 pliarynx in the sense intended by Savigtiy, althougJi lie Jiiistook it for one. 



