IN THE LARV^ OF ANISOPTERID DRAGONFLIES. 



163 



tubercles are more prominent and sharply pointed than in most Libellulid 

 genera, and are very clearly seen in profile under a low power. 



Basal Pads. — One o£ the most striking differences between the Lamellate 

 Type o£ gill and all other forms is the presence of large basal pads belonging 

 to each lamella. These are easily to be seen under a very low power (in 

 Synthemis with the naked eye), because of their deep semi-transparent 

 brownish or orange-brown colour. They were first discovered and described 

 b}^ Sadones. If a complete everted gill-basket be examined, it will be seen 



Text-fig. 14. — Hemicordulia tau, Selys. 

 A single lamella from a full-grown larva, viewed from the anterior or upper surface. 

 Camera-lucida drawing. (x80.) b, base of insertion of lamella; bp, basal pad; 

 ee, external edge of lamella ; es, secondary efferent trachea ; ie, internal edge of lamella ; 

 V, vortex of capillaries. 



that one of these basal pads is attached to each of the gill-lamellse, except the 

 first one or two and the last four or five in each hemibi'anch. (Usually also 

 one can find one or two lamellae near the middle, here and there, which lack 

 them also.) 



The basal pads are a series of rounded disc-like swellings formed in the 

 rectal epithelium at the base of each lamella. They lie towards the outer 

 ends of the lamellse on the anterior or upper border. 



The complete study of these interesting organs, which, although not 

 visible as separate entities in any except the lamellate type of gill, occur in 



