130 PROCEEDINGS OF THE ACADEMY OF [Jan., 



A larva 8 mm. long gliows considerable difference in the size and 

 number of the teeth (PL IV, fig. 2(i). The anterior groups of 

 both fields show an increase in the number of teeth, which remain 

 approximately the same in size. In the posterior groups the 

 smaller teeth show decrease in size with increase in number; the 

 two large teeth of the larger fold remaining the same in size. 



A larva of 10 mm. length shows much the same structure. 



Three larvte of 15 mm. length show the same line of develop- 

 ment carried a little further (fig, 27), an increase in number of 

 the teeth of the anterior groups of both folds, slight increase in 

 number with continued decrease in size of the small teeth of the 

 posterior groups of both folds. 



In all larvie studied the gizzard was found in the second ab- 

 dominal seguient. 



Young images of Ischnura verticalis were examined soon after 

 metamorphosis. In those dissected directly after the spreading of 

 the wings only the larval gizzard was observed. This lay in the 

 sixth segment. In an adult in which the coloring was distinctly 

 developed, the larval gizzard lining lay immediately within that 

 of the adult, which latter bore a very different armature (PI. Ill, 

 fig. 17). In still other individuals the adult gizzard was in the 

 sixth segment, while the lining of the larval gizzard and of the 

 fore-gut of the larva, coiled up in a mass, lay in the lumen of the 

 canal in the seventh segment. These observations suggest the 

 possibility of learning something of the structure of the gizzard 

 of the larva) of exotic species by inspecting the contents of the 

 alimentary canal of imagos whose colors show them to have but 

 recently transformed. 



To sum up the development of the gizzard lining in Ischnura 

 verticals, it is seen that from its earliest appearance (which in the 

 present study was found in a larva 3 mm. long) there is a steady 

 increase in the number of teeth on oil folds with a deciease in size 

 in those of posterior groups. At metamorphosis the gizzard 

 moves backward from the second to the sixth abdominal segment. 

 A new chitinous coat is formed on the fore-gut, with a new gizzard 

 armature. The larval lining lying within the adult lining becomes 

 loosened from it and finally separates entirely, and is found, within 

 a few hours after metamorphosis, lying coiled up within the canal. 

 It is probable that in still older imagos the cast-ofi larval gizzard 



