062 Mr. O. A. Sayce on Three 
3. Compensation for loss of eyesight.—For loss of eyes one 
would expect to find some specialization of other sense-organs 
or in some way a compensation. So far as touch is con- 
cerned this is apparent in the species under consideration, as 
is shown by the following table of measurements of the 
eminently tactile antenne as compared with the nearest 
known allies possessing eyes; but in this relation it is 
important to bear in mind that these allies are not of close 
affinity except in the case of P. gracilis. 
In the following table the length of the body of each species 
ts taken as 100, and the antenna in relative proportion :— 
Phreatoicordes gracilis, § ... a Phreatoicus australis, $...... a 
i Pen 
Niphargus pulchellus ........ a Neoniphargus montanus...... eas 
Janirella pusilla, S ....e.e ee i Janiropsis breviremis, S...... se 
As to the question whether there are a greater number of 
setee generally over the surface of the body and legs, and also 
of olfactory and auditory sete, than in allied species with 
functioning eyes, I think it is not so in the species under 
consideration ; it is, however, hard to judge, but at least I 
have not observed any notable increase of either simple or 
specialized sensory sete. 
The shape of the body of both P. gracilis and N. pulchellus 
is rematkably slender by comparison with other surface allies. 
This has been observed by Chilton in his two subterranean 
species of Phreatvicus. He says, “In the two species of 
Phreatoicus, P. typicus and P. assimilis, the body is more 
slender and the antenne and legs longer, especially in 
P. typicus, than in the surface species P. australis” (1. p. 262). 
An explanation for which he offers: “ It appears probable 
that, in the case of species living in underground waters, the 
greater slenderness of the body has been acquired in order to 
adapt the animal for its life in the restricted spaces between 
the stones and shingle in which it has to live.” 
General Considerations. 
In the orders to which the three species under consideration 
belong the normal forms possess eyes; we must conclude 
therefore that atrophy has taken place in the ancestors of the 
blind species. Packard, who has given earnest consideration 
to and investigation of the cave-fauna of North America, 
publishes in an extensive paper a list of blind or eyeless 
