124 



appear from the surface and fasten themselves to the water plants or to the sides 

 of the aquaria. They are also to be found at the bottom of the water, lying on the 

 dorsal side, supported by the apex of the sipho and the long hairs of the head. 

 At temperatures near zero it can be observed that the larva, often for more than a 

 fortnight, never alter their position; this is also the case if the surface of the aquaria 

 is covered with a slight layer of ice. The larvae never or only at rare intervals seek 

 the surface; they only satisfy their respiratory claims by means of cutaneous re- 

 spiration; the anal gills are spread out, and the large flabella maintain the water 

 currents. 



In these hibernating larva? it is interesting to observe how the number of 

 strokes with the flabellae quite automatically increases or diminishes with the rising 

 and falling temperatures. At a temperature of 3° C. all larva? had the flabellae drawn 

 in; at a temperature of 5 to 6° C. the number of strokes per minute was 30, at 

 temperatures between 14 and 20° C. the number of strokes increased to 114 and 

 when the sunbeams fell directly upon the larva?, to 136. As the water in winter is 

 extremely clear and contains very little detritus or animalcules, the larva? get ex- 

 tremely little food by means of the flabella\ In the winter-larva? we therefore also 

 observe very few swallowing movements, easily observed under the binoculary aqua- 

 rium microscope in autumn or spring. During the winter the flabellae therefore 

 serve mostly for respiratory purposes. 



More than any other of our mosquito larvte the larva? of C. morsitans live 

 upon suspended detritus and plancton ; only rarely we see the larva brush off the 

 plants from the bottom; the flabella? are not suited for that, being quite destitute 

 of comb-hairs. In autumn we And the large larva? hanging down from the surface; 

 the head is held almost horizontally; in large elegant curves the antenna project 

 from the head, and the large antennal tufts form beautiful wheels on both sides of 

 the head; the large flabella are almost always in activity striking in summer 120 

 to 140 strokes a minute and offering an excellent opportunity to study the feeding 

 processes and other phenomena connected with them. I refer the reader to pag. 16 — 19. 



The larva are fastened to the substratum by means of two curved hooks on 

 the flaps of the closing apparatus of the sipho; this is sufficient when the substra- 

 tum consists of small twigs or leaves; on the sides of the aquaria the hooks do 

 not yield the necessary hold, the manner of attachment is then commonly another. 

 It may be observed that the larva often swim round with a little air-bubble at the 

 apex of the sipho; when the larva arrive at the sides of the aquaria this bubble 

 is drawn in, and they are then glued to the aquaria' by means of the diminished 

 space and the pressure of the air. 



Undoubtedly the green waterplants are of the greatest significance to the larva 

 during the winter. In shallow, slowly running brooks, with the bottom covered with 

 carpets of Callitriclie and other green water plants, I have observed that the plants 

 carry hundreds of C. morsitans larva, even where the ice covers the surface of the 

 water, and the plants are partly frozen in the ice. In sunshine little air-bubbles rise 



