MEMOIRS 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 ivith 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 in 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 ( Hypoclithon ), 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 reached the grade of completion which is sufficient for orientation in the 
twilight. 
The very great enlargement of the eyes in several deep-sea fishes, corresponding to the want of light, does not 
occur in cave animals. It is scarcely significant in the species of the genus Sphodrus living in the outermost chambers 
of caves. But, on the other 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 refraction, conductive and sensitive prop¬ 
erties. The 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 retinal 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, and 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 mycrophihalmus) 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 
micro-orthoptera have a greater number of small eyes only perceptible in a very strong light. The Podurid Anurop- 
torus stillicidii 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 Yirchow-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 reconnait effectivement qu'il perjoit 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 trouve alors assis h 
l’entrte d’un de ses couloirs, la ttte droite, tcoutant attentivement de tous cdtts; au moindre bruit il relhve plus 
encore la tSte, puis disparalt immtdiatemeut 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 2-1) 
