LAKES AND TARNS 147 



The Dragon Flies that we see flying over tarn and 

 pond or river are oftenest males; the females usually 

 lead a quieter life among the herbage. The eggs are 

 in most cases laid in gelatinous masses in the water, 

 and sink to the bottom as the jelly dissolves away. 

 The larvae are extraordinarily voracious and have a 

 long youth, often lasting for about a year, sometimes 

 for several years. Very remarkable is a protrusible 

 food-catching " mask," really the third pair of mouth- 

 parts, which the larva shoots out with great rapidity 

 on passing animals. During the long larval period 

 the air-tubes, or tracheae, used in breathing, have no 

 openings, else the creatures would drown, but water 

 passes in and out of the hind end of the food canal, 

 and many kinds have also got threadlike or platelike 

 " tracheal gills." In both these ways the oxygen in 

 the water passes into the closed tracheae and is carried 

 by them into every hole and corner of the vigorous 

 body. Eating much, growing steadily, the larva has 

 to moult its husk over and over again. This moulting 

 is the tax the creature has to pay for its armour, 

 which, being without living cells, cannot grow, and is 

 always becoming- too small for the animal inside. 

 There are sometimes over a dozen of these moults. 

 At the last one the larva creeps out of the water on 

 to a reed or branch and the winged Dragon Fly 

 emerges, often at or near the dawn. 



There are a few Trout in the tarn, how introduced 

 we do not know. We have seen them leaping at 

 Midges in the evening, and one of them that we 

 caught, with an expert's assistance, had its stomach 

 full of the small Water Snail (Lymnaus). There are 

 a few Newts, too, and the spawn of Frogs and Toads 



