138 THE WONDER OF LIFE 



with other species which do serious damage among herds 

 of cattle in the valley of the Danube and in the United 

 States. 



The larva of Simulium reptans lives in rushing water, 

 holding on to water-buttercup and the like by a clawed 

 sucker at the posterior end of the body. It has a similar 

 sucker on the thorax, and it seems to use this one when it 

 moves about on the weed. Another safeguard is to be 

 found in its ability to exude an attaching thread from its 

 salivary glands. It is about 12 mm. long, of a greenish- 

 black colour, and it is continually wafting food into its 

 mouth by the action of two pairs of beautiful sweepers. 

 The larva pupates in a silken pouch or cocoon fixed to the 

 weed, and showing a pair of projecting respiratory processes. 

 Professor Miall describes the emergence of the winged fly 

 from the sub-aquatic cradle, and how it is wafted up to 

 its appropriate element as If inside a large water-bubble 

 an ingeniously simple device ! 



Nets of Caddis Larvae. C. Wesenberg-Lund has 

 given a very interesting account of the peculiar nets made 

 by the larvae of some of the Caddis-flies of lakes and 

 streams. They serve for the capture of the drifting plank- 

 ton. Some are trumpet- shaped, up to four inches in 

 length, with the mouth always upstream. They are bluish- 

 green in summer because of the Algae on the threads, 

 and brownish in winter because of the diatoms. Other 

 nets are flat, with an aperture in the centre leading down 

 into a tunnel beneath a stone ; others are like swallows' 

 nests and are fastened in large numbers to the vertical 

 banks ; others are funnel-shaped and fixed to the pond- 

 weed leaves ; others make chains of baskets out of duck 

 weed leaves and spin a web on the front of each. The 



