MEMOIES OF THE NATIONAL ACADEMY OF SCIENCES. 129 



The following observations are taken from Dr. Joseph's rather rare paper, and are introduced 

 here because they contain novel observations and bear more or less directly on the topic now under 

 discussion. 



Remarks by Dr. Joseph (Erfahrungen, etc., 1882) on the coincidence of partial darkness (1) with the change of position 

 (Lageveranderung) ; (2) decrease in size, arrest of development icith increase in number ; (3) decrease in size without increase 

 in number; (4) loss and compensation for the loss of organs of sight. 



(1) The at least considerable result iu the effects produced by a partial want of light, such as is peculiar in 

 certain rooms in caves, in which the darkness is not total at noon when the sun is highest, but for several hours of 

 the day, mostly in summer (from 11 to 2 o'clock), is that there prevails a kind of twilight, which causes a 

 change of position of the eyes. The twilight enters not from above but from the side into the chamber, while the 

 roof is concealed by continual night-like darkness and radiates not the least light. In adaptation to this circum- 

 stance the eyes in Cyphophthalmus duricorius are not, as in its allies (Phalangium, Opilio, Troglus), placed in the middle 

 of the upper side of the cephalothorax, but on the ends of projections on the side of the cephalothorax. The 

 creature therefore has acquired the faculty of seeing sidewise and of moving as readily sidewise as backward. The 

 flattened form of many Chernetidse which live under the bark of trees, whose eyes are also situated on the side of 

 the cephalothorax, show that similar results of adaptation occur outside of caves. Similar corrective aims seem to 

 underlie the tendency in the eyes of Cyphophthalmus to project from the level of the sides of the body. 



(2) The diminution in the size of the eyes in a great number of cave animals (Hypochthon), the fish of Mammoth 

 Cave, and a considerable number of Arthropods (beetles, flies, Orthoptera, Arachnids, Isopods, and Myriopods) forms 

 an opposition to the correction of changed light relations. 



The correction for the partial want of light seems here to be abandoned. Another remedial principle of adapta- 

 tion has prevailed. The eyes have only readied the grade of completion which is sufficient for orientation in the 

 twilight. 



The very great enlargement of (he eyes in several deep-sea fishes, corresponding to the want of light, does not 

 occur in cave animals, h is scarcely siguilii-ant i:i I he species of the genus Sphodrus living in the outermost chambers 

 of caves, liiif. •■!] the oilier hand, the diminution in extent of the circumference of the eyes by arrest of development 

 is demonstrated, and is accompanied by the reduction of light-collecting refractiou, conductive and sensitive prop- 

 erties. Tiie small eyes of the cave triton, overgrown with the transparent skin, are provided only with a deficient 

 musculature insufficient for adequate movements. The chorion contains only a small pigment layer, and the outer- 

 most thin layer of retiual rods corresponds with the sparse fibers of the feebly developed optic nerve ; features which 

 characterize the reduced eyes of the mole and blind mouse. In an analogous way the reduced eyes of several genera 

 of beetles (Trechus, Bythinus, etc.) living in twilight seemed to undergo an arrest of development, since only from 

 50 to 80 corneous facets, crystalline lenses, aud rods are associated together, while these organs in allied genera living 

 in the upper world may be counted by hundreds and thousands in a single eye. The reduction is carried still further 

 in certain spiders (Nictyhyphantes mycrophthalmus) and certain species of Myriopods and Asellids, whose eyes retro- 

 grade to simple diminutive, spider-like eyes, while their open-air allies are endowed with compound eyes. 



Before this reduction reaches a complete absence, there seems in certain spiders and Podurids a sort of rise in 

 number to serve as a correction to the partial want of light. The diminution and arrest of the eyes by this retarding 

 influence becomes compensated by a multiplication of the same organs. Troglohyphantes shows sixteen, and several 

 inicro-orthoptera have a greater number of small eyes only perceptible in a very strong light. The Podurid Anurop- 

 torus siillicidii described by Schiodte possesses twenty-four scarcely visible eyes. 



(3) By constant residence in perpetually dark chambers the influence of disuse at work destroying the develop- 

 ment of organs of sight completely prevails, and the possibility of sight has wholly disappeared. 



The blind cave fauna is associated with the subterranean and deep-sea fauna, consisting of a 

 considerable number of genera and species. The author refers to an earlier publication in Heft 

 228 of ihe Virchow-Holzendorf collection of popular scientific tracts, wherein he remarks: 



(1) The discovery of extinct Arthropods inclosed in copal, amber, and the Solenhofen slates proves that in the 

 earlier geological epochs a very considerable number of blind genera and species have inhabited more numerous and 

 varied localities than in the present period of the earth's history.* 



(2) Blind species could only maintain themselves where, as in the perpetual night of caves, the issue of the 

 struggle for existence neither was nor is based on the possession of organs of sight. 



galeries a disparu ; mais le conduit auditif persiste largement ouvert et l'oreille interne, organe essentiel de l'audition, 

 est normalement constitute. 



Si l'on observe le Spalax vivant, on reconnalt effectivement qu'il percoit les sons avec la plus grande facility. 

 Pour le surprendre hors de son terrier, il fant s'en approcher avec une extreme prudence: on le trouvo alors assis a 

 l'entrde d'un de ses couloirs, la tete droito, e"coutant attentivement de tous cdtes ; au moindre bruit il releve plus 

 encore la tete, puis disparalt imm&liatement sous le sol (Duchamp, pp. 38, 39). 



* This may be an overstatement, since on mentioning Joseph's remark to Dr. Hagen, who in past years has paid 

 so much attention to insects occurring in amber and copal, he writes me he knows of no eyeless amber or copal 

 insects, except that "the very rare soldiers and workers of Termites in amber are blind." 



S. Mis. 30, pt 2 9 



