Notes on some Microscopic Organisms. 
25 
chemically considered, as the enclosing cell-wall of the Desmidiae, 
and commonly known as cellulose (a term, by the way, used in an 
extremely loose and indefinite manner), and is possessed of con- 
siderable tenacity, as will be seen to be the case farther on, and is 
evident by the fact that we can handle the filament quite roughly 
without tearing the cells asunder : thus it is common to find this 
plant growing in running water where it withstands the flow of 
the stream. The mode of reproduction known to exist is, as far as 
I can learn, by the shrinking inwards of the inner cell-membrane, 
commonly known as the “ Primordial Utricle” of Mohl, and en- 
closing the cell-contents away from the tough cellulose coat, while, 
at the same time, the cell-contents themselves assume a more or less 
coarsely-granular condition, apparently from the enlargement of the 
individual particles of which it is made up. It is recorded that 
thereafter, at a certain period in this change, the outer cell-wall 
splits across at a point near to one end of the cell, and, while the 
lid so formed remains attached to one side the other and largest 
portion, the cell-contents escape from the cavity into the surround- 
ing water, and gradually assume the spherical form. Thereafter 
there is developed upon one side of the sphere a ring of ciliae which 
become more and more active until, at last, they move about with 
such energy that the little green globe assumes an extremely active 
motile condition, flying about for some time in such a lively manner 
that an observer meeting with it and unaware of its origin would 
certainly be inclined to rank it within the confines of the animal 
kingdom. In this state it has been called a “ motile spore,” but 
we will see, farther on, that it hardly can be ranked as an ovum in 
the ordinary acceptation of the word. 
Up to this period our record, as hitherto published, is complete ; 
but just here is a gap, and it has been my good fortune to make 
such observations as fill it and complete our knowledge of the life- 
history of this plant. It is known, however, that the motile con- 
dition just described is but transitory, and perhaps it may have 
been on account of the velocity of its movement, and the conse- 
quent difficulty of keeping it under observation, that the next step 
has not, as yet, been observed. In some unknown way, then, it has 
been supposed that the active spherical form assumes the static 
condition, develops rootlets or filaments, which serve to attach it 
to other objects, and then, being fixed, it thereafter by means of the 
usual well-known method of cell subdivision develops into a new 
filament resembling exactly the parent plant from which it sprung. 
As I have said, I have been enabled to show how the motile form 
is changed or, more properly speaking, developed into the static 
form, and, at the same time, I think, ’’throw some light upon an 
important portion of microscopic biology. The changes and trans- 
formations which I herein record, I have seen not merely a few 
