ZOOLOGY. 329 



back and sides, from the similarly tinted weeds among which that 

 fresh water shark lies at the watch, as motionless as they. Even 

 when a tearing old trout, a six or seven-pounder, sails in his wanton- 

 ness, leisurely up stream, with his back-fin partly above the surface, 

 on the look out for a fly, few, except a well entered fisherman, can 

 tell what shadowy form it is that ripples the wimpling water. But 

 the bellies of fish are white, or nearly so ; thus imitating in a degree 

 the color of the sky, to deceive the otter, which generally takes its 

 prey from below, swimming under its intended victim. Nor is this 

 design less manifest in the color and appearance of some of the largest 

 terrestrial animals ; for the same principle seems to be kept in view, 

 whether regard be had to the smallest insects, or the quadrupedal 

 giants of the land." 



Prof. Agassiz has stated that the coloration of the lower animals 

 living in water depend upon the condition, and particularly upon the 

 depth and transparency of the water in which they live ; that the 

 coloration of the higher types of animals is intimately related to their 

 structure ; and that the change of color which is produced by age in 

 many animals is connected with structural changes. Coloration is 

 valuable as an indication of structure ; and it is a law universally 

 true of vertebrated animals, that they have the color of the back 

 darker than that of the sides ; and that the same system of coloration 

 prevails in all the species of a genus, partially developed in some, but 

 recognizable when a large number of species is examined. 



MICROSCOPIC LIFE. 



PROFESSOR EHREXBURG, of Germany, lays down the following 

 positions as the result of his long and laborious researches : 



1. That microscopic life, in the forms constituting earth and rock, 

 appears to exist in the same manner ever the whole earth. 



2. That everywhere, in all climates, zones, elevations, depths, and 

 in the smallest particles of humus, microscopic life not only exists but 

 abounds. 



3. That there is such a relation between European microscopic 

 organism, and those of other parts of the earth, that new orders, 

 classes, and families, are nowhere found, but the forms all belong to 

 the generally silicious and non-silicious. 



4. There are also found in soil and calcareous strata everywhere, 

 undecomposed parts of larger organisms, either silicious or calcareous, 

 of vegetable and animal origin, closely resembling in character the 

 flora or fauna of the localities. 



5. There are peculiar local genera, not numerous, and also numer- 

 ous peculiar species of widely distributed genera. 



(J. Certain geographical latitudes have their characteristic forms of 

 minute animal life. 



7. All over the earth there is distributed a considerable number of 

 perfectly identical forms. 



8. The so-called inorganic constituents of the body and shells ol 



