THE 
AMERICAN NATURALIST. 
VoL. x11.— JUNE, 1878. — No. 6. 
A LESSON IN COMPARATIVE HISTOLOGY. 
WITH PLATE IL 
BY CHARLES SEDGWICK MINOT. 
‘Oe of the first scraps of information which a young naturalist 
is apt to acquire, when he learns something of the history of 
zoology, is the knowledge of the great names of Linné and 
Cuvier. The reforms effected by these two great men in the 
methods of studying animated nature would alone secure them 
enduring. fame; when we reflect, however, that they also labored 
industriously to add to our knowledge, and were successful as 
investigators as well as reformers, we must yield to the conviction 
_ that the honorable prominence assigned to them among natu- 
ralists is their just due. After both Linnzus and Cuvier had 
been dead for years, a German savant made a discovery concern- 
ing the elementary structure of plants, which revealed the fact 
that all the parts of plants are built up out of the same units, 
which have ever since been called cells. This great generaliza- 
tion is now taught to every botany class as one of the funda- 
mental principles of vegetable anatomy and physiology, and the 
name of its great discoverer, Schleiden, is generally coupled with 
it. Schleiden made the results of his investigations generally 
known in the year 1837; and it was only two years later that his 
friend and countryman, Schwann, published a memoir showing 
that the same units—the cells—are found in all animals as well. 
It is a familiar fact to all, in these days when natural science 
has penetrated to the schoolhouse and the magazines, that matter 
Consists of molecules, or minute particles, which are themselves 
composed of other particles still more minute—the atoms. 
Every mass of matter is made up of molecules, and indefinite _ 
numbers of molecules seed be added to a mass without ee - os 
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