896 THE AMERICAN NATURALIST.  [Vou, XXXIII. 
Archiv für Entwickelungsmechanik der Organismen, seventy-two 
pages, with six plates, part of them colored, and ten figures in the 
text. 
In this memoir Dr. Eigenmann describes the degraded condition 
of the eyes in the six known species of the Amblyopside, three of 
them (Chologaster cornutus, C. papilliferus, and C. agassizii) with small 
but developed eyes, and three, Améblyopsis speleus, Typhlichthys sub- 
terraneus, and Troglichthys rose, being blind. ‘The blind species are 
not very close to one another, and each must have been independ- 
ently derived from eyed forms. Typhlichthys is descended from 
Chologaster, the others from genera now extinct. 
After an exhaustive study of the anatomical details, Dr. Eigenmann 
takes up the causes of the degeneration of the parts of the eye, and 
their replacement in the orbit by masses of fat. He considers in 
detail the theory that the organ diminishes with disuse (ontogenic 
degeneration) and that the effect of disuse appears to some extent in 
the next generations (phylogenic degeneration). 
A second theory is that of panmixia, the cessation of selection in 
which the general average falls progressively the birth average as 
maintained in selection. 
A third is a reversed action of natural selection, by which the 
organ degenerates through the migration of those with good eyes to 
the light, or through their extermination on account of the waste in 
weight or nutrition, or through injury to the useless eye. 
Still another view is that of the struggle of the parts either for 
room or for food. By this the unused eye may be crowded out or 
starved. 
Another view refers the degeneration of the organ to a struggle 
between soma and germ to produce the maximum efficiency of the 
former with the minimum expenditure of the latter. 
Or again we may suppose that the result follows, through germinal 
selection, the struggle of the representatives in the germ. 
Dr. Eigenmann calls attention to the fact that while we ought to 
consider, first, the causes of individual generation and, second, the - 
processes or causes which led to its transmission, practically it is im- 
possible todo so. Again the eye is itself a complex organ, and when 
each of its parts loses its utility, the degeneration progresses un- 
equally. His final conclusion is, that “the condition of the eyes in 
_ the blind fishes can only be explained as the result of the transmis- 
sion of disuse effect.” The eye (functional) of Chologaster is sym- 
metrically reduced from a larger normal fish eye. The retina is the 
