i6 Outline of Life-history 



builds its case ; the Orthocladius-larva appears to rely 

 almost solely on its own secretion. It feeds voraciously 

 on the surrounding Spirogyra, and the filaments which 

 are interwoven are those which have already passed 

 through its alimentary canal. 



' On account of the transparency of its tube, the larva 

 of Orthocladius is a convenient form for study. Its 

 activities are : (i) Feeding. A filament of Spirogyra is 

 seized by the mandibles and bitten in two. Then the 

 labrum, beginning at one end of the filament, draws it 

 into the gullet by a stroking action. In the case of 

 Spirogyra condensata, amongst which the larva was first 

 obtained, a filament was very soon eaten, but when 

 aS^. ortliospira was supplied, the feeding was much slower 

 and apparently more laborious, j)robably on account of 

 the thick gelatinous sheath of this alga. If there is no 

 food near, the larva, clinging to the tube by its anal feet, 

 projects far out, and sweeps rapidly around until it gathers 

 in a fresh wisp of filaments. In captivity, when the 

 food-supply is exhausted, it will feed on other filamentous 

 forms, e. g. Oedogonium. From time to time, the larva, 

 protruding the tail-end from the tube, evacuates a bolus 

 of digested Spirogyra, which at once disperses. This was 

 rather surprising until microscopic examination showed 

 that the filaments are not masticated, but simply crumpled 

 up, and the contents removed, except remnants of the 

 green protoplasm, so that when the filaments are released, 

 the elasticity of the cell-wall straightens them out. 

 (2) Respiration. The larva, when lying in its case, waves 

 its body up and down ; this sets up a current of water, 

 which flows in at the front-end and out behind ; either 

 end may be the front-end, as the creature often reverses 

 its position. The action is quiet and leisurely. (3) Loco- 

 motion. As the case is not fixed, the larva can travel 

 without leaving it. It does not creep like a caddis-larva, 



