46 



G. F. HILL. 



is a black, chitinous, angular projection of the upper anterior margin of the labrum 

 and is the most conspicuous feature of the first instar. Graber's organ is visible on 

 the posterior portion of the tenth segment as a pair of dark, pyriform, closely 

 approximated bodies. 



Second Instar. Since most of the characters found in the larvae of the second 

 instar are visible through the cuticle of, and appear to belong to, the first instar, the 

 changes which follow the first ecdysis do not appear to be so great as they are in realit}-. 

 Fixation in hot alcohol after the first ecdysis is completed and in all subsequent stages 

 of larval development has the usual effect of extending the body to its fullest length ; 

 thus, whereas the length of a larva of the first instar is about 1-40 mm., the length 

 just after moulting is about 1 -00 mm. greater. The measurements, descriptions and 

 figures which follow are all from specimens fixed in hot 70 per cent, alcohol, and 

 therefore fully extended. The characters of the larvae of the second instar are shown 

 in fig. 3, which represents a larva between one and six hours old. Such larvae range 



Fig. 3. T. apvepcs, anterior end of larva 1-6 hours 

 old (above) ; posterior end of same (below). 



from 2-33 mm. to 2-63 mm. in length, by 0-375 mm. to 0-425 mm. in width at the 

 widest part ; the segments bear distinct longitudinal striae ; the anterior border of 

 each segment, excepting the first three (thoracic), is fringed with numerous small 

 bristle-like hairs and dense short brown pile, which produce the banded effect (seg- 

 ments four to nine inclusive resemble the tenth segment shown in fig. 3). The first 

 three (thoracic) segments are shown in fig. 3. The mouth-parts are prominent ; the 

 first maxillae, palpi, and antennae are easily distinguished ; the anterior projection of 

 the labrum is rounded and no longer black and chitinous ; four malpighian tubes are 

 distinguishable ; Graber's organ still contains one pair of bodies, which are now seen 

 to be enclosed in a pyriform sac, the rounded end of which is foremost ; the apical 

 third of the syphon tube bears two groups of three long slender hairs, which usually 

 appear to arise at the extremity owing to invagination of the apex and withdrawal 

 of the stigmal plate. 



During the 16 or 17 hours following the first ecdysis there is little apparent change 

 in the young larva other than a slight increase in size and, generally, the addition of 

 another pair of bodies in Graber's organ. A long series of larvae of this age measured 

 from 2-35 mm. to 2-82 mm. in length, bv 0-35 mm. to 0-425 mm. at the widest part. 



