IN THE LARV^ OF ANISOPTERID DRAGONFLIKS. 



161 



The general arrangement o£ the gills is easily understood from text- 

 figs. 11, 12. Each holobranch consists of two exactly similar hemibranchs, 

 symmetrically arranged about a middle line or axis running midway between 

 them. Each hemibranch consists of a single row of gill-lamellse, ranging in 

 number from twelve to nearly thirty, according to the genus selected. The 

 bases of insertion of these lamellpe are arranged slantwise to the long axis 

 of each holobranch, with their anterior ends close to that axis and their 



Text-fig. 11. — -Synthemis 

 macro stigma, Selys. 

 Portions of three hemibranchs 

 from the everted gill-basket of 

 a full-grown larva. Lamellate 

 Type. The middle and left- 

 hand hemibranchs belong to 

 one holobranch. The right- 

 hand hemibranch is seen in 

 profile from its outer side. 

 Basal pads shown in black. 

 Semi - diagrammatic, drawn 

 from a whole mount. ( X 30.) 



Text-fig. 12. — Di-placodes hcematodes^ Burm. 

 One-half of the complete gill-basket, everted, 

 from a full-grown larva. Lamellate Type. Pig- 

 mentation omitted. Basal pads shown in 

 black, mostly seen by transparencj' through 

 the overlying anterior lamella. Right-hand 

 holobranchs in profile. Semi-diagrammatic, 

 drawn from a whole mount. (X30.) 



posterior ends removed from it. Hence the gills in each holobranch appear 

 to slant away posteriad from the middle line in symmetrical pairs, one on 

 either side of it. It is quite clear, from a comparison of this figure with that 

 of the Undulate Type in the Simplex System, that these gill -lamellae repre- 

 sent highly-differentiated cross-folds of an originally Simplex System — for 

 they agree exactly with them both in position and direction. The base-lines 

 of the gills of one hemibranch are, as a matter of fact, intermediate in level 



