184 



THE RESPIRATORY SYSTEM 



[CH. 



capillary loops. The free end of the papilla is armed with strong 

 hooks. Pigment of a deep brown, purplish or even blackish 

 colour is strongly developed in the foliate type. The total number 

 of capillaries in the gill-basket of Anax reaches 100,000 or more. 



(3) The Lamellate Type (fig. 79 E, F; fig. 80, 8-n). This 

 beautiful and unique type occurs only in the Libellulidae, with 

 little variation throughout this immense family. Each gill is in 

 the form of a separate flat lamella, set on a broad obliquely-placed 

 base (figs. 81, 82). The number of gills in a hemibranch is from 

 twelve to thirty. Near the anterior outer corner of the base of 

 each gill is a prominent rounded disc of an orange or brown colour, 



tv 



Fig.81. A single lamella from the gill-basket of Hemicordulia tau Sflys( x87). frpbasal 

 pad ; e z secondary efferent ; lam blade of lamella ; tv tracheal vortex. Original. 



the basal pad (bp). The secondary efferent trachea of the gill 

 breaks up, beneath the base, into a number of strong tracheae close 

 together. From each of these there comes off a whole brush or 

 pencil of capillaries, which run up to the oval tip of the gill, and 

 then turn inwards to form the very characteristic appearance 

 called the tracheal vortex (tv), finally returning to join other pencils 

 of capillaries. 



