364 



PSYCHE. 



The maxillae are always free except 

 at their very base : they possess a 

 basal sclerite, never separable into 

 cardo and stipes, a palpus always well- 

 developed and 4 or 5-segmented, and a 

 single maxillar lobe, which is wanting 

 in a few cases. When present, this 

 lobe is a slender, elongate, weakly- 

 chitinized, thin, flat, process, with 

 pointed and " fringed" apex. It shows 

 gradual degrees of reduction to total 

 disappearance. 



The labium is a free, short (but little 

 longer than broad) under lip, with 

 basal sclerite only rarely showing 

 indications of its composition of two 

 parts (sub-mentum and mentum) and 

 with terminal lobes showing various 

 degrees of coalescence with each other. 

 The base of the labium is in some 

 instances united by membranes with 

 the bases of the maxillae. Palpi are 

 always wanting ; no unmistakable indi- 

 cations of them are to be found, al- 

 though in two forms examined, what 

 may be palpar rudiments are present. 

 The terminal lobes in freest condition 

 consist of the two free paraglossae 

 sometimes apparently 2-segmented, and 

 a median, always delicate, membranous 

 lobe representing the fused glossae. 

 The paraglossae when free, as is the 

 condition in almost all the Nematocera, 

 show no indications of pseudo-tracheae 

 and are rather thick, concave on their 

 inner faces, and more or less thickly 

 beset with hairs of varying size and 

 strength. In one family the paraglossae 

 tend to coalesce, and within the limits 



of this one family (the Tipulidae) the 

 paraglossae may be found free, partly 

 coalesced and coalesced almost com- 

 pletely. With the beginning of coales- 

 cence, appears the first indications of 

 pseudo-tracheae, and in the nearly com- 

 pletely coalesced condition, the system 

 of pseudo-tracheae is well developed. 



The hypopharynx is probably always 

 present (in one or two instances I have 

 been unable to dissect it out satisfac- 

 torily on account of its minute size and 

 delicacy). It is a delicate, membra- 

 nous, elongate, pointed plate, in which 

 the course and opening of the salivary 

 duct can usually be seen. It is always 

 free from its base, arising from the 

 inner (upper) wall of the labium to its 

 tip. 



Homologies and Phvlogeny. 



The homologies of the various mouth- 

 parts within the group Nematocera 

 seem obvious and certain. The differ- 

 ences between the mouthparts of Blepha- 

 rocera, Simulium, and Ceratopogon in 

 which mandibles and a functional maxil- 

 lar lobe are present, and the mouth- 

 parts of Bibio and Tipula in which there 

 are no mandibles and no maxillar lobe is 

 simply one of degree of specialization 

 by reduction. Sinailarly the single, 

 broad lobe with elaborate system of 

 pseudo-tracheae which constitutes the 

 labium of Tipula simply presents the 

 extreme degree of coalescence (as 

 reached among the Nematocera) of 

 the outer terminal labial lobes, the para- 



