ADJUSTMENT OF ORGANISMS TO ENVIRONMENT 413 



a microscope. The accompanying figures (fig. 241) will 

 assist in identifying all the structures present. 



The record for this study may be in the form of sketches 

 and diagrams of the respiratory apparatus studied. 



FIG. 241. Diagram of the gill chamber of the nymph of a dragonfly (Anax 

 junius) from drawings by Miss Elizabeth Andrews, a, cross section of the 

 gill chamber; d, d, dorsal tracheal trunks; v, v, ventral trunks; /, tuft of 

 filamentous gills; m, longitudinal muscle; b, a single gill filament, showing 

 tracheae and tracheoles. 



Study 54. The comparative development of respiratory 

 apparatus in aquatic insect larva. 



Materials needed: Either preserved or fresh specimens 

 of larvae of the following: Ceratopogon, or some other gill- 

 less form (perlid or trichopter will do as well) . 



i. Two or more dipterous larvae having blood gills of 

 different sort: Chironomus (the larger "blood worms," 

 with ventral abdominal gills) and Simulium will be best. 



