266 DR. C. CHILTON ON THE SUBTERRANEAN 



quoted by Sjience Bate [1, i. p. 321], Nipliargus fontanus " soon dies if exposed to 

 the light." This is certainly not my experience with the New-Zealand forms : I have 

 kept all the species, except Phreatoicus, for longer or shorter periods in glass bottles, in 

 which they could get no shelter, exposed to the full light of day ; and if the water was 

 properly aerated, they appeared to live without inconvenience. As stated above, species of 

 Cruregens fontanus have thus lived for five months. In the same bottle I afterwards 

 kept a specimen of Gammarus fragilis, wliich appeared quite at home, but then un- 

 fortunately died during an unsuccessful attempt to moult its exoskeleton. It had no 

 shelter from the ordinary light of day, and made no attemj)t to hide itself ; if placed so 

 that the strong light of a lamp was focussed on to it by the convex surface of the bottle 

 it, however, moved away. I did not notice anything peculiar in its habits ; it usually 

 crawled around at the bottom of the jar or along the stems of the plants in the bottle, 

 but at times swam freely like ordinary Amphipods. 



There is very little more to record concerning the habits of the Cruregens. The animals 

 usually crawled about on the bottom or along the stems and leaves of the Ruppia 

 mariUma ; they could not, however, crawl up the vertical sides of the bottle, the glass 

 being too smooth for them ; they ran backward and forward with equal rapidity, and 

 did not seem particular which way they went ; they did not swim, but if they dropped 

 off the plant wriggled helplessly till they reached the bottom. I did not notice any- 

 thing that would indicate any power of vision, but, on the other hand, often saw them 

 running against objects in a way which seemed to indicate that they were totally blind ; 

 occasionally I have seen two approach very near each other, apparently without being 

 aware of it, and then suddenly jump apart when one touched the other. 



IX. The Bearings of the Phenomena of Subterranean Life on the 



Theory of Descent. 



It has been early recognized that the phenomena of cave and subterranean life have an 

 important bearing on the Theory of Descent. Here the conditions of life are so peculiar, 

 so abnormal, the fauna so scanty, and its environment so simple and so i-estricted that we 

 may naturally expect to find the problems that are to be solved presented to us in their 

 simplest forms. Thus we have no vegetable life of any kind except a few fungi, only a 

 comparatively small number of animals of various groups, and these surrounded by con- 

 tinual night and exposed to a temperature probably pretty uniform from year to year ; 

 in many cases we can tell, with at any rate a fair approach to accuracy, from what 

 surface-species the underground species has descended ; and knowing also, within certain 

 limits, the age of the latter, we can estimate the changes undergone and consequently 

 the rate at which these have been made in this jiarticular instance. 



The importance of Isolation in securing permanence of type in the case of cave- 

 dwelling animals has been dwelt upon by Packard [83, pp. 14jO-14<1]. Similar remarks 

 would apply with perhaps even greater force to the subterranean fauna, such as that of 

 the underground waters of the Canterbury Plains, for it is probably even more com- 

 pletely isolated from the surface-fauna than is that of caves. 



