149 



soluble substances from the food, this power being possessed 

 throughout this part of the alimentary canal and not confined to 

 a special zone, as Cuénot had previously determined for fat 

 absorption in Orthoptera, while fore- and hind-guts do not 

 absorb. The peritrophic sac is apparenth" the inner surfaces of 

 the epithelial cells, which become detached when these cells are 

 in active secretion. Experimental evidence was also given for 

 the eliminating action of pericardial cells, heart-walls, and 

 Malpighian tubes. 



That very characteristic organ of Odonate larvœ, the labium 

 or mask, has been the subject of a special study, embryological 

 and comparative anatomical, by Miss Butler (1904), from 

 which the conclusion is drawn that the lateral lobe represents 

 merely the labial palpus while the middle lobe is formed of 

 laciniai and galeae more or less consolidated in the different 

 groups. This is essentially the theory of Rambur (1842) and 

 of Hagen (1854), in opposition to that of Gerstacker (1873), 

 Heymons (1896), and Borner (1909). 



Length of Larval Life. 



It was not until 1909 that any definite statements existed 

 as to the actual length of larval life and the number of moults 

 passed through by the Odonata. Li that year, Balfour- 

 Browne gave the results of rearing Agrión pulchellum and 

 I schnür a elegans from the egg to the imago, the first and only 

 species for which such a complete developmental record has yet 

 been published. He found, however, that the number of moults, 

 consequently the number of larval stages, or instars, and the 

 total length of larval Hfe arc not constant even in the same species. 

 After distinguishing the form which leaves the egg and which 

 has not free limbs as the pronymph, and counting as the " first 

 nymphal" stage that which follows, the pronymphal moult, 

 Balfour-Brovvne found that in Agrión pulchellum the trans- 

 formation to the imago ma}- follow the tenth, eleventh, twelfth, 

 or thirteenth larval (n3'mphal) stage. The shortest time which 

 elapsed from hatching of the egg to the emergence of the imago 

 in this species was 230 days ; another individual occupied 634 

 days. The body-length in the last larval stage varied from 14 



