WATER RELATIOlSrS OF OTHER SPECIES 



137 



§ 47. Insects 



The quantitative exchanges of water can scarcely be represented 

 for a single species of insects, for appropriate data are lacking. 

 The qualitative nature of the gains and losses of water, and the 

 tolerance of water deficits, have been outlined for various insect 

 orders by Buxton ( '32b). In turnover most gains are said to occur 

 by specific drinking of water, though some kinds do not habitually 

 touch free water. Most losses are believed to be evaporative, ex- 

 cept those in water excesses. 



The impression might be obtained that the water contents are 

 much less uniform in insect species having non-aqueous environ- 

 ments than in frogs or earthworms. So far it has no quantitative 



■•■100- 



+50 



12 3 4 



Hours 

 Fig. 84. Course of water load ( % of Bo) after ingestion of rabbit blood. Bhodnius 

 prolixus, 1 individual of 78 mg. at 18° C. The insect took 225% of Bo of blood, or 

 169% of Bo of water. The load plotted is water ingested minus urine expelled (sen- 

 sible load) ; an additional 10% was lost insensibly in 4 hours. Data of Wigglesworth 

 ('31a, p. 414). 



support. Variations among analysed individuals are not greater 

 than in some vertebrate species and many invertebrate ones (see 

 table 19). 



Much information indicates that insects do something about a 

 water increment, whether it be a deficit or an excess. For the for- 

 mer, there is no controlled evidence, only surmise, that drinking by 

 mouth is increased by water deficits (Buxton, '32b, p. 277; Mel- 

 lanby, '38, p. 399). For the latter, data concerning excretory re- 

 covery of water content are shown in Rhodnius, a blood-sucking 

 bug (fig. 84) after one sudden excess of water (along with other 

 substances) has been taken in the form of rabbit blood. The water 

 is presumably eliminated through Malpighian tubules. 



