800 The American Naturalist. [October, 
the forms which would be found in a very great area. This 
resulted in the invention of the “ Müller Net,’ a small gauze — 
net which is drawn through the water, entangling in its meshes 
the very minute and delicate organisms. For a long time 
Miiller and his students pursued the study of marine forms, 
and at length came the discovery that the marine fauna and 
flora was directly comparable to the terrestrial. 
Yet little is known of the laws of the distribution of marine 
life. The laws of the distribution of the terrestrial fauna and 
flora have been formulated for animals in the classical works 
of Wallace and for plants by Griesbach. The famous “ Chal- 
lenger” expedition (1873-1876), under the direction of Sir 
Wyville Thompson and Dr. John Murray has given us the 
largest conception of the wealth of marine life, and has laid 
the foundations for the study of the marine forms both at the 
surface and in the depths of the ocean. Dr. Murray in his 
preliminary report called particular attention to the enormous 
wealth of organic life not only at the surface, but also many 
hundred fathoms below. He says that when living forms were 
scarce on the surface the tow net usually disclosed very numer- 
ous forms below, even to a depth of 1000 fathoms or more. 
In the North Pacific Ocean the discovery was made that zones 
of definite depth are characterized by animals and plants 
peculiar to them. The tow nets sunk to 500, 1000 or 2000 
fathoms brought up forms never found within 100 fathoms of 
the surface. The animals characteristic of these different 
depths are, for the most part, of the class of Radiolorians, 
those microscopic organisms whose silicous skeletons form 
much of the soft ooze which carpets the bottom of the deep 
sea. Prof. Haeckel, by study of this material was led, in his 
monumental work on the Radiolaria, which forms a part of 
the “Report of the Challenger,” to the recognition of three 
groups, (a) pelagic, swimming at the surface of the calm sea; 
(b) zonary, swimming in definite zones of depth (to a depth of 
more than 20,000 feet); (c) profound (or abyssal) animals swim- 
ming immediately over the bottom of the deep sea. In gen- 
eral the different characteristic forms correspond to the 
different zones (up to 27,000 feet). 
