136 



PHYSIOLOGICAL EEGULATIONS 



The only known difference between Limax and Helix with re- 

 spect to water exchange is related to the fact that the latter can 

 prevent loss of water by evaporation, deficits arising but slowly 

 during hibernation or non-locomotion. During hibernation the 

 body fluid gradually increases in concentration of dry residue, re- 

 covering its initial concentration suddenly upon emergence and 

 shedding of the epiphragm (Holtz and Brand, '40). 



Though Helix loses water very slowly during inactivity, in 

 ordinary existence its weight fluctuates by (CA) ± 8% of Bo in 

 daily periods (Howes and Wells, '34). Water loss is therefore not 



-60 -50 -40 -30 -20 -|0 



Water Load 



Fig. 83. Eate of initial gain of water (% of Bo/24 hours) in relation to water load 

 (% of Bo). Terrestrial shelled snail, Eelix, three species, 9 individuals. From each 

 body weight (0.4 to 19 grams) the weight of the shell has been subtracted. Privation 

 of water lasted 6 to 12 months; then water was available for 24 hours. Data of 

 Kiinkel ('16, p. 120 ff.). 



slow during usual activity. Probably the fluctuations depend upon 

 water intake, for when food but not water is supplied, Httle ir- 

 regularity of weight is found. Helix, then, usually does not drink 

 water so frequently as once a day, as though it is insensitive to 

 deficits of AW - 8. That picture of inconsistency in Helix is not 

 borne out by the extensive study of analyzable water contents made 

 by Brand ('31), for it would have been expected from the above 

 facts that individuals analyzed at one time would vary by (C.V.) ± 

 8%. If Helix be an animal that regularly has a wide range of water 

 contents ; it is not representative of invertebrates generally. 



