ee a Notes on Diatomaceex. hy) 
tubes; this species, consisting of naviculiform frustules enclosed 
and freely swimming about in tubes, after the manner of Schizonema. 
In fact there is nothing to separate these genera, except that the 
first inhabits fresh water, whilst the latter is an inhabitant of the 
sea, where it is to be found generally in profusion, covering larger 
aleze and rocks. The extension of the tube takes place after the 
following manner. As the frustules increase by the process of sub- 
division common to all of the Diatomacez, of course the two frus- 
tules thus formed occupy double the space of one, and as the cell 
division is continually going on, after a time the tube must become 
choked with individuals. At this period in their existence they 
appear to be extremely active, moving with increased rapidity up 
and down the tube as freely as their crowded condition will permit. 
Whether the end of the tube is never closed, or opens at certain 
seasons, I have been unable to determine; at all events it is now 
found to be open, and the frustules slip over each other until they 
reach this opening, and one or two will project outside as if pro- 
specting, and will occasionally return within the general envelope. 
When a frustule thus projects from the open end of the tube, it 
never, as far as I have seen, rushes onward with the vigorous 
motion with which it moves within the envelope, but this is doubt- 
less only so when the tube is being lengthened. It can be easily 
understood that if the species be disseminated by the distribution 
of perfect frustules, as seems to be most likely, that they must then 
escape from the tube after the manner I have recorded above as 
taking place in the allied genus, Schizonema. When one or two 
frustules have projected from the open end of the tube, they often 
immediately come to a rest just beyond the tube, or do so after 
moving over each other slowly outside of, but in a line with, the 
tube. While at rest there appears to form around them a trans- 
parent mucous sheath, which, so that it may not fix them in their 
position, is kept in a tube form by the frustules again moving over 
each other, and thus, as it were, fashioning and smoothing the 
inside of the tube. This sheath becomes more and more dense, 
until it is plainly visible as forming an elongation of the tube, when 
the frustules again project from the end, and a new portion is added. 
I have in this way seen a tube grow across the field of the micro- 
scope, and the closely-packed frustules extend themselves in single 
file, each just overlapping those in front and behind it. The mem- 
brane constituting the tube, although dense and strong, is somewhat 
elastic, but not very much go, for I have seen three or four frustules 
become wedged together by one attempting to pass backwards whilst 
the others were moving forwards, and at such times the tube does 
not stretch to accommodate the crowding, but yet is often bent by 
the force of the moving frustules. In fact this force must be con- 
siderable, as is evidenced by the size of the obstacles, as grains of 
