602 RESPIKATOR^• ORGANS OF JJKAGON-FLV LARV.^i. 



trunks, which are connected to the dorsal ones caudally. V 

 " post-dorsal " trachea ]jasses to the extreme caudal gills. 



Two African Libellulids, 'Framca and Pantala, deserve l)rief 

 notice. In Tramca the gills grade upwards regularly in size 

 passing caudad. In Pantala the caudalmost five gills are very 

 large, and all the gills carry setce. In all other genera the gills 

 or villi or folds are of practically one size throughout. 



Let us turn to the Zygoptera now. These larvae have no 

 res],iratory rectum, Ijut just behind the Malpighian tubes is an 

 enlarged ampulla, with three fatty pads much tracheated. There 

 is record of Zygopteran n^^mphs drawing water into the recttun. 

 but the organ for res])irino^ therefrom has thus far been un- 

 discovered. 



The physiology of the dragonfl\- lar\ al res])iratory system is 

 simple. Chitin, as shown by Dewi'tz, 1890, is water-impervious, 

 but allows oxygen and carbon dioxide to diffuse freely. In the 

 gills or villi there is only chitin between water and the air in 

 the trachese. The metabohsm (>f the animal produces high partial 

 pressure of carbon dioxide and low partial pressure of oxygen 

 in the tracheal air: the fi*i"iipr diffuses out into the water, the 

 latter in therefrom. The movements of the animal kcej) the 

 tracheal air in circulation, even if diffusion alone were not stiffi- 

 cient to pass oxygen to the cells and carbtm dioxide away fiDm 

 them. 



Mature larvae possess open spiracles on the thorax, and can 

 breathe air directly as well as Tia the water. At metamorphosis, 

 the res])irator\- part of the rectum shrivels up and its trachese 

 vanish. 



THE A.^S(KT.\TI()X OF GAME WIT!! i^SETSE-FLY 

 DISEASE IX ZULULANI). 



Bv Danid '!"iio.\i.\s .Miti iirli., M.K.C.WS. 



(Not printed.) 



X H.\C'!"I":!<IAI. Sl*()-|- ( )!•■ CI'I RES. 



Hv IvniKi. .\l AK\ Doinoi-;. M.A.. !).Si., IvE.S. 



(!'rinled in llic Annals (.f .Vjyplied Biologv. \'ol. Ill, Nos. 2 

 and 3. January. \*-)\y.) 



CriRES CANKER IN SOU'l'll A!' RICA. 



P.y Ivnii-i. A!.\K\ Doiix;].:, M.A.. D.Sc, F.L.S. 



(Printed as HiilJriin \'o. 20. ndT.. of Union of South Africa 

 Ih'parlincnl i>( . h/riculturr.) 



