34 



Comparative Animal Physiology 



the body fluid adapts to the medium (Fig. 26). The tolerance of saHnity 

 depends on the medium in which the larvae are reared. Larvae of Aedes 

 argenteus reared in fresh water are killed when they are transferred directly 

 to 1.1 per cent sodium chloride or to sea water diluted to the equivalent of 

 1.3-1.4 per cent NaCl, whereas if the concentration is increased gradually the 

 larvae are able to live in these media. The anal papillae of Culex pipiens 

 larvae reared in 0.65 per cent NaCl are very small; when they are reared in 

 0.006 per cent NaCl, the anal papillae are larger; when 'the larvae are reared 

 in distilled water the anal papillae are very big and the epithelial cells may 

 become vacuolated. The anal papillae of Aedes detritus larvae in Algerian 

 ponds of a salinity equivalent to 1.2T0 per cent NaCl are smaller than those 

 of larvae of A. aegypti from fresh water.-*' The larva of Chironomus th.um.mi, 



Fig. 17. A, Hind end of larva of the mosquito Aedes aegypti, reared in salt water, 

 showing sohd uric acid in lumen of malpighian tubes. B, The same larva, a few minutes 

 after transfer to fresh water; the malpighian tubes have been flushed out by water entering 

 through the anal papillae, a, mid-gut; h, malpighian tubes; c, hind-gut; d, anal papillae. 

 From Wigglesworth.""" 



unlike the larvae of Aedes and Ctdex, takes in water over its entire body 

 surface. '-^^ 



The anal papillae of Chironomus larvae avidly take up silver from dilute 

 solutions of silver nitrate, '■^** and the anal papillae of Aedes aegypti take up 

 electronegative dyes. ^^^ After a period of salt deprivation the anal papillae 

 actively absorb salt from dilute solutions (0.01 Ringer solution ).^''*^' ^'*-' -^^ 



The function of the anal papillae is clear. They are not respiratory but are 

 salt-absorbing mechanisms. Their permeability to water is a necessary condi- 

 tion to salt absorption. The body surface is more permeable, especially to 

 water, in Chironomus larvae than in Cidex and Aedes, but in the larvae of 

 both groups the anal papillae become enlarged and actively absorb salt when 

 in a dilute medium. The urine as formed in the malpighian tubes is similar 



