41 2 EMERfiENCE 6F DRAGONFLY-LAkVyE, 



Oil. No observatiuu.s appear to ha\ e been made, up to the 

 present, on newly hatched or \ery young larvse. 



Asa general rule, the caudal gills of newly-hatched ZygopLerid 

 larv;« are exceedingly slender, almost filiform, and fringed with 

 long, delicate hairs, few in number and irregularly placed. 

 Whatever may be (»ur o[)ini()n on the efficacy of these organs at 

 a later period, when they have taken on their tinal form, and 

 tle^ eloped within themselves a rich tracheal system, nobody, we 

 suppose, would claim that they are very efficient organs of respira- 

 tion in the newly-hatched larva. If we combine this well-known 

 fact of the slender and weak formation of these organs with the 

 results of the experiments carried out in Section 2 on the larva 

 of Anax (experiments which, one can scarcely doubt, must hold 

 good for the great majority of dragoiiHy lai'Vio), we see at once 

 the reason for the vigorous rectal respiration carried on in tlie 

 case of our Zygopterid larvic during the first half-hour after 

 hatching. It is xoi merely aih ordhtary act of resplrallon, bat is 

 necessary /or the quick rcplacemeibt of t)ie CO^ in the tracheal 

 system by air. Once the tracheal system has reached the normal 

 state, so that the necessary supply of oxygen to the tissues is 

 assured, rectal respiration will be governed, in larvtB of different 

 kinds, by the efficacy of the total of other respiratory activities. 

 Respiration through caudal gills, through lateral abdominal gills 

 when they occur, and througli the integument in such cases as it 

 may occur, all differ from rectal respiration in heing practically 

 coiifinaous, carried on without special efforts on the part of the 

 lar\a. Consequently, if the caudal gills have a poor tracheal 

 sup})lv, or a very tough integument, or if the general integument 

 of the larva be unsuitable for respiration by diffusion, the call on 

 the larva for rectal pulsations must be heavier. If the caudal 

 gills are accidentally lost, we should expect that the rate of rectal 

 respiration woidd be increased. Similarly, we might e.xpect to 

 find a higher rate of rectal respiration towards the end of each 

 instai-, when the general integument tends to become tough and 

 hard, than at the beginning, when it is soft and delicate. Ex- 

 periments along these lines should lead to. interesting conclusions 



