iS 



somewhat longer than the first pair, and, again, both pairs on the 

 same individual may approach the maximum or the minimum in 

 length. Toward the end of this stage, traces of the first and third 

 pairs of dorsal spines of the third instar may be observed beneath 

 the dorsal surface of the body. The first pair of spines arise directly 

 beneath the bases of their ontogenetic predecessors, and are directed 

 forward obliquely so that the two cross near their tips, in the middle 

 line of the body. The developing third pair of spines are directed 

 backward and outward, and like the first pair arise beneath the base 

 of their predecessors. The segmentation of the abdomen is fairly 

 distinct in the middle, while that of the thorax is more obscure. 



The vasiform orifice (Plate III, Fig. 10) is relatively farther for- 

 ward in this instar than in the preceding one, which is indicated by 

 the comparatively greater distance from the apex of the orifice to the 

 caudal margin of the body, and by the fact that the spines on the 

 dorsum near the orifice now lie opposite the operculum, instead of 

 anterior to it, as in the first instar. The vasiform orifice is of about 

 the same general form as in the first instar. The operculum lacks 

 the tooth-like process on each side of the caudal margin, and is pro- 

 portionately longer than before, extending nearly one-half the dis- 

 tance toward the apex of the orifice. The lingula is spatulate, with 

 two pairs of side lobes and one terminal lobe. When in its natural 

 position its caudal end reaches to about three-fourths the distance 

 from the anterior to the posterior end of the orifice. On each side 

 of the terminal lobe arises a spine which extends backward to a little 

 beyond the apex of the orifice. A smaller spine arises on each side 

 between the two side lobes. The upper surface of the lingula bears 

 about fourteen longitudinal rows of minute seta;. The apical half 

 of the operculum and the lingula are more opaque than the other 

 parts of the body. The chitinous ridges which bound the orifice 

 laterally do not meet behind, although the intervening space between 

 their ends is comparatively smaller than in the previous instar. 



The eyes are proportionally smaller than before, and are situated 

 internally instead of at the surface as in the first instar. The eyes 

 on each side are about on a line with and outside of the two dorsal 

 spines (first pair) on the cephalic region. 



On the ventral side of the body (Plate II, Fig. 7) the vestigial 

 legs and antenna; can be plainly seen, their relative position being 



