196 RECTAL BREATHING-APPARATUS IN ANISOPTERID DRAGONFLY LARVAE. 



However, on examining them nine days after they were laid, on Feb. 22nd, 

 I found about two hundred newly-hatched larvse in the dish. Some of these 

 were quite transparent and freshly hatched. The gill-basket is very peculiar. 

 It is of the Simplex Undulate Type, the main folds being clearly developed. 

 Each main fold is brownish in colour and very short. On either side of it, 

 only one or two cross-folds are developed. These are well supplied with 

 tracheal capillaries, and are already recognizable as lamellae by their size, 

 shape, and inclination to the body-axis. No ecdyses having so far occurred, 

 I cannot say definitely how the increase in the number of lamellse takes 

 place. From the position of the gill-basket, it seems likely that the first- 

 formed lamellas are the hindmost, and that others will be developed from 

 behind forwards. 



The above observation justifies the phylogenetic conclusions at which I 

 had already arrived, that the Simplex Undulate Type is the most primitive 

 type of Anisopterid rectal gill. At the same time, it marks off the Lamellate 

 Type as very distinct in its origin, and apparently developed at an earlier 

 period in the history of Odonata than were the other Duplex Types found in 

 the yjEschnince. — R. J. T. 



