MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 137 



As regards the origin of the deep-lake fauna of Switzerland, Forel, in his Faune Profonde 

 (4 me se>., 1879, p. 500), concluded as follows: 



1. The lake fauna of our subalpine regions descended from animals which have immigrated since the glacial 

 epoch. 



2. From the fact that they are immigrants from other regions they have all had to adapt themselves to the 

 special conditions of each lake. 



3. The immigration was made for each of the tbree fauna? in a particular way, viz: 



a. Littoral fauna : by the passive migration of animals already adapted to lake life from other lakes, and by 



the active migration of animals having asceuded the rivers and having consequently had to adapt 

 themselves on the spot to a lacustrine life. 



b. Pelagic fauna : by the passive migrations of auimals already adapted in other lakes to the lacustrine life. 



c. Beep-lake fauna : by the active or passive migration of animals coming from the littoral or pelagic faunae 



of the same lake and having undergone on the spot an adaptation to the environment. 



Lastly, in his Essai sur la faune profonde des lacs de la Suisse, 1885, Dr. Du Plessis-Gouret 

 substantially adopts Forel's view, which he quotes. He also remarks: 



The animals of the abyssal regions have originated by direct emigration from those which peopled the shores; 

 and the former have themselves been brought into the lakes by running water under the form of affluents of all 

 kinds, or by the staguant waters of marshes aud ponds communicating with the lakes by means of freshets. En 

 resume, our littoral lacustrine fauna is only a simple particular case of the fauna of running and stagnant waters of 

 the surrounding country, and consequently the deep-lake fauna is but a special offshoot of the littoral fauna, like a 

 part of the pelagic fauna, which has in a similar -way detached itself from the animal life of the shores. 



It appears, then, to recapitulate, that while the blind fauna of the world is but an almost infini- 

 tesimal portion of animal life as a whole, it is characteristic of the totally dark abysses of the ocean 

 and of lakes as well as of caves. But while the deep-lake fauna and that of caves is generally con- 

 ceded to be no older than the Quaternary period, that of the ocean abysses is probably much 

 older, and directly descended from the Tertiary and even the Cretaceous periods, though it is 

 believed with good reason by certain zoologists that all deep-sea life originally emigrated from 

 the waters of comparatively shallow depths; namely, within depths less than a thousand fathoms- 



THE BEARINGS OF CAVE LIFE ON THE THEORY OF DESCENT. 



So far as we are aware, Lamarck was the first naturalist to refer the atrophy of eyes and loss 

 of vision to disuse from a life in darkness, as may be seen by the following extract from the chapter 

 ju his Philosophie Zoologique entitled " De l'iufluence des circonstances sur les actions et les habi- 

 tudes des animaus, et de celle des actions et des habitudes de ces corps vivans, comme causes qui 

 modifient leur organisation et leurs parties." This work appeared in 1809, many years before the 

 discovery of blind animals peculiar to caves. 



Des yeux a la tete sout le propre u'un grand noinbre d'animaux divers, et font esseutiellement partie du plan 

 d'organisation des verte'bre's. Deja n6anmoins la taupe, qui, par ses habitudes, fait tres-peu d'usage de la vue, n'a 

 que des yeux tres-petits, et a peine apparens, parce qu'elle exerce tres-peu cet organe. 



L'Aspalax d'Olivier (Voyage en Egypte et en Perse, II, pi. 28, fig. 2), qui vit sous terre comme la taupe, et qui 

 vraisemblableinent s'expose encore moins qu'elle a la lumicre du jour, a totalement perdu l'usage de la vue ; aussi 

 n'offre-t-il plus que des vestiges de l'organe qui en est le siege; et encore ces vestiges sont tout-a-fait caches sous la 

 peau et sous quelques autres parties qui les recouvrent, et ne laissent plus le moiudre acces a la lumiere. 



Le protee, reptile aquatiqne, voisin des salamandres par ses rapports, et qui habite dans des cavit6s profoudes et 

 obscures qui sont sous les eaux, n'a plus, comme l'Aspalax, que des vestiges de l'organe de la vue; vestiges qui sont 

 couverts et cache's de la meme maniere. 



Voici uue consideration decisive, relativemeut a la question que j'agite actuellement. 



La lumiere ne pe"netre point partout; cOnse'quemment, les animaux qui vivent habituellement dans les lieux oh 

 e lle u'arrive pas, mauquent d'occasiou d'exercer l'organe de la vue, si la nature les en a munis. Or, les animaux qui 

 font partie d'uu plan d'organisation, dans lequel les yeux entrent n^cessairement, en ont du avoir dans leur origine. 

 Cependant puisqu'on en trouve parmi eux qui sont privds de l'usage de cet organe, et qui n'en ont plus que des 

 vestiges cache's et reconverts, il devient 6vident que l'appauvrissement et la disparition meme de l'organe dont il 

 s'agit sont des re"sultats, pour cet organe, d'un deTaut constant d'exercice (2d edit., i, p. 241). 



In his ''Origin of Species" Darwin, after claiming that "natural selection would constantly 

 aid the effects of disuse" in the case of moles and the burrowing rodents, then remarks in regard 



