BY n. J. TILLYARD. 91 



gests that, during the whole of the day, they must remain 

 in the dark, horizontal mud-channels, or low down in the 

 vertical channels — a conclusion which is justified by the 

 positions in which we actually found them. 



What then is the value of the more numerous channels, 

 such as a^, Uo, and bi, opening at the tops of the clumps I 

 These are used for the final emergence. But, as they were 

 found in good condition on November 5th, before any of the 

 larvae had emerged, they must have other uses. I think it 

 possible that the larva may undergo each ecdysis above 

 ground, probably during the night-time. It is also very likely 

 that they come up these channels each night, and wander 

 about looking for food. 



The only other larvae found, while searching for Petalura, 

 were five larvae of Synthemis macrostigma, two small and 

 three nearly full-fed. These lie, just covered, in the mud of 

 the depressions. The letters X in the diagram indicate the 

 position. It is doubtful whether the Fetalura larvae ever 

 capture them, except when they are very young. Had either 

 of those I examined been feeding on them, the labium of 

 Synthemis could not fail to have appeared in its gizzard. 



Structure of the teeth in the gizzard. — The second point, 

 and by far the most important, is the arrangement of- the 

 chitinous teeth in the Petalurine gizzard. Although nearly 

 all the larvae taken, appeared to be very ill-nourished and 

 flabby, yet in both the specimens examined (I selected the 

 two healthiest) the stomach and gizzard were very large. The 

 latter was qviite 4 mm. long, of the usual bottle-shape, the 

 neck being about 1 mm. in diameter, and the anal end quite 

 3 mm. This, when carefully cleaned, cut and spread out 

 flat on a slide, stretched out into a thin, transparent mem- 

 brane in the shape of a trapezium with a base of 10 mm., 

 top 4 mm., and slant sides 10 mm., and convexly curved. No 

 sign of teeth could be observed, either with the naked eye or 

 with an ordinary pocket lens. Under a magnification of 25 

 diameters, the teeth appeared, close up to the neck of the 



