140 NATURAL HISTORY OF AQUATIC INSECTS CH. 



of the larva. The larva has red blood, and burrows 

 in mud at the bottom of streams and pools. The 

 pupae of such species have two bunches of respiratory 

 filaments. The second group, which is called by 

 Meinert the Motitator Group, is found at the surface 

 of the water on confervae, floating logs, etc. The 

 larva has no respiratory tubules ; the blood is usually 

 colourless ; the pupa has respiratory trumpets instead 

 of filaments. 1 



The origin of these two groups can only be 

 conjecturally traced. Both probably originated in a 

 Tipulid, which as a larva burrowed in the earth and 

 breathed air, and as a pupa was provided with two 

 respiratory trumpets opening by a very narrow cleft, 

 like those of Tipula. We may suppose that such a 

 larva betook itself to damp earth in the neighbour- 

 hood of streams, and gradually become more and 

 more aquatic. Subsequently a divergence of habit 

 arose in the aquatic forms. Some of the larvae 

 frequented the bottom of the water, while others 

 preferred to live at the surface. The bottom-feeders 

 developed the hollow tubes on the eleventh segment 

 as organs of aquatic respiration, and also haemoglobin 

 in the blood, as a means of storing up oxygen. Those 

 which took to life at the surface of the water, finding 

 oxygen easy to [obtain, were able to dispense with 

 both tubules and haemoglobin. Each group has its 

 characteristic pupa. One is adapted for living at the 



1 Our knowledge of the early stages of Chironomus at 

 present extends to a very few species, and we do not know 

 whether the \vhole genus can be divided into these groups, nor 

 if so, how many species belong to each. 



