ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
273 
Under the theory of natural selection, however, the vast body of facts 
becomes at once intelligible. “ Here the accumulated facts of the most 
diverse kind, which receive an intelligible explanation by the theory in 
question, yield a firm support to the theory. There are many theories 
which are held upon indirect evidence of precisely the same nature. 
We believe in evolution, not because we see it taking place, but because 
of the immense number of observed facts which it renders intelligible.” 
At the same time a considerable amount of direct evidence of the action 
of natural selection in relation to mimicry and common warning colours 
is already forthcoming. 
Function of Pyloric Caeca in Teleostei.* * * § — Th. Boudouy finds that 
these tubes have considerable digestive importance. In Merlangus pol- 
lachius and Motella mustela the secretion digested fibrin and hydrated 
starch ; in Mugil chelo (herbivorous) there was no digestion of fibrin, 
but a saccharifying of starch. 
Laws of Morphology.f — Prof. Paul Jaccard discusses organic form 
and its causation. He distinguishes two main factors in evolution : — first, 
the action of the environment, which is said to produce adaptive vari- 
ation varying according to the stage of evolution in which the organism 
occurs, but not to be the cause of evolution ; second, physiological 
division of labour, which is the prime cause of evolution, and is the 
result of the properties of living matter. To this the adaptive vari- 
ations are subordinate. This thesis is illustrated in detail. 
Resemblance between Arctic and Antarctic Marine Eaunas4 — 
Prof. D’Arcy W. Thompson has subjected the “ bipolar hypothesis ’ to 
searching criticism, and decides emphatically against it. He finds that 
the evidence of the specific identity of northern and southern forms is 
very weak ; it will not hold for Tuuicates, Holothurians, Crustaceans, or 
fishes. “ We have found no single species of fish, of Decapod, of Isopod, 
no certain one out of a large fauna of Amjjhipods, to inhabit at once the 
Arctic and Antarctic oceans, or the regions adjacent thereto. Moreover, 
apart from specific identity, it has not been shown that similar and truly 
allied forms give to the two regions a common facies.” 
Origin of Cave Faunas.§ — Mr. C. H. Eigenmann publishes very 
brief abstracts of several papers on the fishes of American caves. He 
has examined numerous members of the Amblyopsidae, some of which 
live in the open and others in caves. He finds that those living in the 
open show marked degeneration of the eyes similar to that which occurs 
in the cave-dwelling forms, but less marked. Some of the cave-dwelling 
forms have mere vestiges of eyes, while others found in the same caves 
have well-developed eyes ; all, when kept in an aquarium, show marked 
avoidance of light. He believes that the degeneration of the eye began 
before the fish entered the caves, and is phyletic and not primarily due 
to the cave habitat. 
Variation in Fishes.|| — Mr. W. T. Moenkhaus has investigated the 
variations of the dorsal and anal fins of JEtheostoma caprodes and Etheo - 
* Comptes Rendus, cxxviii. (1899) pp. 745-6. 
t Bull. Soc. Vaud., xxxiv. (1898) pp. 402-27 (5 pis. and 8 figs.). 
X Proc. Rov. Soe. Edin., xxii. (1898) pp. 311-49. 
§ Proc. Indiana Acad. Sci., 1897, pp. 229-31. || Tom. cit., pp. 207-28. 
