190 A]Sr ESSAY ON" THE DEVELOPMENT 



ever, the lower ring is complete — i. c, the two halves of the stipes have become 

 united. That it must be stipes is shown by the fact that it bears the palpus, and 

 again the surmounting selerite must be maxillary also. 



There are other species allied to those already cited in which similar structures 

 occur ; but I need for the present call attention to only one more ; a species of Olfersia 

 (PI. II, Fig. 19). Here the ring is complete in front, but broadly open behind, and 

 bears the chunky, single-jointed palpus. Surmounting is a single selerite, very much 

 resembling in appearance that of I'teromaliis, and undoubtedly homologous with it. 

 Of course Olfersia is parasitic in habit, and the mouth parts are specialized for blood- 

 sucking; but the sclerites composing them are nevertheless derived from the same 

 source as in the " higher " types. 



I have several times referred incidentally to Simulium, and of this the galear 

 structures are figured ( PI. I, Fig. 1"). Dissecting the paits out carefully we find an 

 almost complete ring at the base, the stipes, to which the palpus and palpifer are 

 attached. Surmounting this is a pair of sclerites, each almost a half cylinder, repre- 

 senting the subgalea, and bearing the two-jointed galea. Here again I claim that the 

 three joints just referred to 'iuust be maxillary because they are directl}" aiticulated to 

 the selerite bearing the maxillary palpi, and the labial structui'es are all shown at 

 Fig. 1". 



A step in the direction of union we find in the Anglesea gnat or midge — also a 

 Simuliid, to which reference has been already made. Here we see (PI. I, Fig. 2') the 

 subgalea united most of their length at one side, while the galear joints are yet free. 

 The basal stipes is not figured because none of my specimens showed it clearly ; but 

 the palpifer, palpus and lacinia. as they are connected with it, are shown in the 

 specimen. 



In the Asilidtti we find another suggestive structure, studied in the light of the 

 facts already set out. Here we see, as illustrated PI. Ill, Figs. 1" and 1'', the basal 

 stipes well developed, united posteriorly, but separated in front. The palpifer and its 

 attached [)alpus are situated at the sides, clearly articulated to the stipes, whose char- 

 acter is thus fixed. Attached to this stipes is a broad, infolded structure, united be- 

 hind but open in front; maxillary because of its attachment to the stipes, and sub- 

 galea from its location. It bears in orderly sequence the two-jointed galea of which 

 the terminal joints are free. The species of the Asilidce are large and easily dissected, 

 and the figures were drawn from a species of La/ihria. The attachments are but 

 little ditferent in the species, and as the figui-es illusti-ate the structure from both 

 front and rear, the position of the joints should be; clear. These figures will be again 

 referred to in another connection. 



