200 



THE RESPIRATORY SYSTEM 



[CH. 



lamellae as a kind of parachute when descending through the water, 

 and that most, if not all, Zygoptera can exist without them. The 

 problem as it stands offers an immense field for interesting original 



research. 







Lateral Abdominal Gills (fig. 87). 



These occur on either side of ab- 

 dominal segments 2-8 in the larvae 

 of Pseudophaea, Bayadera, and Aniso- 

 pleura, and on segments 27 of the 

 larva of Cora [31, 62, 104, 137]. Their 

 position is distinctly ventral, and they 

 appear to be remnants of true paired 

 abdominal appendages, serially homo- 

 logous with the thoracic legs. In shape 

 they are slender filaments. Bis [137] 

 states that their internal structure in 

 Pseudophaea resembles that of the 

 saccus, except for the extreme attenu- 

 ation of the organ. The alveoli are 

 few in number, and moss-like fibrils 

 are absent. 



E. Movements of Respiration. 



In the imago of the Dragonfly, the respiratory movements can 

 be followed with ease, by holding the live insect in the hand by 

 means of its wings. The broad-bodied Libellulinae are the best 

 for this purpose. Inspiration is effected by an increase in the 

 volume of the abdomen, the sternites being lowered and the tergites 

 expanded latero-ventrally. At the same time the whole abdomen 

 becomes slightly lowered. By this movement, air is drawn into 

 the spiracles. The act of inspiration is brought about simply by 

 the relaxation of the transverse or dorso-ventral muscles of the 

 abdomen. 



The converse movement, that of expiration, is brought about 

 by the contraction of the transverse muscles. By it the abdomen 

 is contracted, the sternites being raised and the tergites narrowed, 

 while the abdomen as a whole is slightly raised. The movement, 

 too, is quicker than that of inspiration. It seems, however, clear 



Fig. 87. Larva of Pseudophaea 

 sp. (x 1 1) to shew caudal sacci 

 and lateral abdominal gills. 

 Drawn from a photograph 

 sent by Dr F Ris. 



