we o DESMIDS AND DIATOMS. 
former, and containing within its cavity the “endochrome,” 
or green coloring matter, which seems to be analogous to 
the chlorophyl or leat-green of the higher plants; and, 
lastly, a thin hyaline membrane enclosing the two former, 
and analogous to a similar membrane among the Diato- 
mace. The surface of the cell thus enclosed is often 
ornamented by the existence of numerous markings, 
strie, lines or dots, but still oftener by the presence of 
projecting points or spines, which give to many of the 
genera a singularly beautiful appearance. In the interior 
of this cell may sometimes be seen a curious movement 
of the cell contents, which has given rise to much discus- 
sion among the students of these forms. Some assign 
the circulation thus witnessed to ciliary action, others to 
the spontaneous movement of enclosed zoéspores ; but as 
this is still a debated point, I shall not at present dwell 
upon it. The same is true of the motion quite commonly 
observed of the whole Desmid through the medium in 
which it lives, with a slow majestic movement, very sug- 
gestive of animality, and which caused these organisms 
to be assigned by the earlier writers to that kingdom. 
The existence of external “cilia,” either in these or in 
the Diatomacex is exceedingly improbable. Like other 
plants, they have a marked tendency to travel towards 
the light, and have sufficient power of locomotion to 
penetrate to the surface of mud in which they have been 
imbedded during the drying up of pools. 
The multiplication of the Desmids is accomplished by 
two methods: by self-fission, or the dividing of the cell- 
contents into two portions, as is commonly the case with 
all Alge ; or, secondly, by a true generative process, “N 
the formation of “Sporangia.” As, however, these pro- 
cesses are very similar to those which characterize the 
