October 



1884. 1 



SCIENCE. 



337 



nocturnal. It might almost be said that there 

 are no ' fixed ' habits. I have found marked 

 variations in every one of the most charac- 

 teristic habits of our birds ; and can see no 

 reason why the same degrees of variability 

 should not likewise obtain among mammals, 

 reptiles, and fishes. In considering fishes as 

 either nocturnal or diurnal, I mean that they 

 are so to about the extent that owls are ; i.e., 

 ranging from species as diurnal as hawks to 

 those that are nocturnal, or, properly speak- 

 ing, crepuscular. How often we hear the 

 phrase, ' as blind as a bat ' ! yet these mam- 

 mals are not averse to daylight, and only shun 

 the glare of noonday. In shad}' woods they 

 are often found insect-hunting by day ; and 

 fly just as freely, and range abroad as gen- 

 erally, on cloudy days, as during the gloaming 

 throughout midsummer. 



etheostomoids, is always to be found, when not 

 in motion, resting upon the bottoms of streams ; 

 and I have never found these fishes in localities 

 where their color did not closely resemble the 

 sand, mud, or pebbles upon which they rested. 

 I have tested them in this matter in the follow- 

 ing manner. Finding a spot in a small stream 

 where man}' of these fishes congregated, I 

 placed a large number of white- porcelain plates 

 in the stream on a level with the surrounding 

 sand. On disturbing the ' darters,' I found 

 that they invariably settled between these 

 plates, and never on them ; and this after the 

 dishes had been several clays in position. 

 Finally the currents covered the plates with a 

 thin coating of sand, and then occasionally a 

 ' darter ' would come to rest upon one of the 

 plates. The motion of his fins in so doing 

 usually displaced the sand, and exposed the 



Mud-minnow {Umbra limi). 



Several years ago, when studying our fishes 

 with reference to detecting supposed traces of 

 voice possessed by them, I concluded that the 

 nocturnal, dull-colored species had the power 

 of uttering certain sounds, especially during 

 the breeding-season ; while the diurnal fishes 

 were apparently voiceless, and were dependent 

 upon their gaudy coloration as a sexual attrac- 

 tion. More recent observations have led me 

 a step farther, and I am convinced that the 

 colors of man}' species continue to play an 

 important part in the struggle for existence 

 throughout the interim from one breeding- 

 season to the next. It must be remembered 

 that fishes, when undisturbed by man's pres- 

 ence, are very different from the frightened 

 animals that rush hither and thither in the 

 most reckless manner when startled by his 

 sudden appearance. We have only to take a 

 favorable position, and, ourselves unseen, to 

 gaze patiently into their accustomed haunts, 

 to realize what animated, cunning, and mentally 

 well-developed creatures fishes really are. 



That curious group known as 'darters,' or 



white surface beneath : if so, the fish darted 

 off, and settled between the plates or beyond 

 them. It is evident, I think, that protection 

 through their color must be quite essential to 

 them ; more so in the matter of procuring their 

 food, perhaps, than as a safeguard against the 

 attacks of enemies. 



The mud-minnow (Umbra limi) depends very 

 largely upon insects and smaller fishes for food, 

 and the question of color is a prominent one in 

 its life history. This fish frequently assumes 

 what we may call an ' inanimate ' position, and, 

 with a variety of colors streaking and spotting 

 its sides, has much the appearance of a bit of 

 dead grass, a twig, or a caddis-worm. Often 

 such unnatural positions will be retained for 

 many minutes, or until some object suitable for 

 food comes within reach, when it darts at and 

 seizes it with the rapidity and certainty of a 

 pike. Now, in all such cases, there is great 

 and constant changing of color. Often the 

 tints deepen until the fish appears to be inky- 

 black, then pale until, from above, we can 

 scarcely detect the fish. Such changes, of 



