I30 THE INTEGUMENTAL SKELETON OE THE IMAGO. 



the mouth is developed in the Diptera nothing was known with 

 regard to it. Weismann failed to detect the rudiments of 

 the proboscis in the young nymph, and although Kiinckel 

 d'Herculais speaks of the appendicular discs of the head, and 

 actually figured them in the resting larva of Volucella, he gives 

 but one figure in which I can recognise the position and rela- 

 tions of the maxillary discs [25, PL 7, Fig. i.//], and in the 

 description of the plate he refers to them as the rudiments 

 of the antennae. He did not, therefore, recognise their real 

 nature. 



I have alread}' described the maxillae of the Blow-fly larva 

 (page '^'j) and the stomal disc. It is from the hypodermis of 

 the stomal disc that the disc at the extremity of the proboscis 

 originates, and as the second pair of maxillae are easily seen 

 in the embryo lying between and behind the first pair, on 

 which the rudimentary stomal disc is apparent, it is plain 

 that the terminal portion of the proboscis of the imago is 

 developed from the first, and not from the second pair of 

 maxillae. 



Robineau-Desvoidy is the only author who, so far as I know, 

 arrived at conclusions which my researches enable me to 

 endorse, but, unfortunately, he gives no reasons for his state- 

 ments, which have received little attention. He says, ' The 

 proboscis of the Diptera, in my opinion, is not formed by the 

 lower lip, as in the Hymenoptera, but by the maxillae. In the 

 Muscidse it is usually membranous, sometimes solid and tri- 

 articulate. The more or less solid piece which covers the 

 groove on the dorsal surface of the proboscis is the labrum or 

 upper lip ' [49, p. 12]. Desvoidy, however, says in the same 

 paragraph, ' Its base is enveloped by the base of the labium, of 



Ukscrii'tion of Plate VI. 



One lateral half of the Proboscis of the Blow-fly divided in the middle line and seen 

 from the cut surface : ps, the palpiger ; /, the palpus ; pi, prelabrum ; /, ligula ; 

 pa, paraphysis ; d s, discal sclerite ; th s, thyroid sclerite ; ep f, epifurca ; s s, 

 sesamoid sclerite ; st, stomal or hypoglossal sclerite ; s v, salivary valve ; f, 

 fulcrum ; tr^ to tr*, trachece ; m^ to tn^, muscles ; s g, salivary gland of the oral 

 disc. Part of the rostrum only is represented, s s to ep f is the haustelium, 

 consisting of the theca, prelabrum and disc. 



