NATURAL HISTORY OF THE DIATOMACEAE. 423 



has been done towards studying the local peculiarities influencing the 

 distribution of these organisms, that we will dismiss the subject with this 

 brief mention, merely pointing out that therein lies a field for investiga- 

 tion which will yield abundant fruit to the patient and conscientious 

 student. 



They are to be found in all permanent collections of water, but have 

 never been observed in pools formed by the rain and liable to be dried 

 up, and they may be looked for at all seasons, although, as might have 

 been supposed, they appear in greatest numbers in spring and during the 

 autumn. The hottest days of summer, at least in such localities as the 

 present writer has examined, seem to be unfavorable to their growth 

 (that is to say, in fresh water), but they have been gathered in midwinter 

 from beneath the ice in the Hudson river, New York. In the ocean we 

 find that season affects the diatomaceae, as it does most organisms which, 

 like them, live near tide levels ; that is, they diminish in numbers as the 

 cold of winter approaches, only to increase again in spring. 



The structure of the diatomaceae is very peculiar ; and althought heir 

 general outline can, without any very great difficulty, be made out by 

 using a magnifying glass of moderate power, their ultimate anatomy is 

 extremely difficult of elucidation, as will be exemplified further on. This 

 can be readily understood when we know that the largest of them are not 

 over eight thousandths of an inch in diameter, and that many, and those 

 by no means the smallest, are only two ten-thousandths of an inch across. 

 If the diatomaceae possess an outer membrane, integument, or, we might 

 almost say, skin, it is extremely delicate, so much so that it has not with 

 certainty been detected as yet, although one or two observers think they 

 have seen something that looks like such a seemingly necessary limiting 

 portion of the individual. But we shall see hereafter that there are 

 organisms very closely related to those we are now considering, which 

 certainly do not possess limiting membranes, but whose whole substance 

 is homogeneous, and made up of but one kind of substance of a semi- 

 gelatinous consistence, and known to naturalists as protoplasm, meaning 

 the simplest of all living matter. It is likely, then, that the diatomaceae 

 have for an essential base to their bodies this protoplasm ; and, reasoning 

 from what we know of allied organisms, it is within and from, in part, 

 the substance of this protoplasm that the other portions of the individual 



