05 
Gomphonema acuminatum and a Cocconema, the species of 
which was not at the time determined, moved about in a 
vigorous manner when found naturally detached, and also 
when freed from their stipes by violence. Again, several 
years ago I made a gathering of Schizonema cruciger, a 
species which consists of siliceous frustules enclosed within 
tubes of membranous material glowing upon other sub- 
merged matter, having its frustules free and swimming 
actively about upon the surface of the water without any signs 
of investing tubes, which, however, were found empty hut 
standing erect and adherent at the bottom of the ditch inha- 
bited by the Schizonema. I have noticed that bare stipes of 
an Achnanthes, without any pendent frustules, are by no 
means uncommon, and also Gomphonema stipes can be found 
in the same condition. In such cases, doubtless, the freed 
frustules might be found near by, and, in fact, I have in 
what may be called “free” gatherings, floating upon the 
surface of the water, observed Cocconeis, Achnanthes, and 
other forms which at one time I was in the habit of classi- 
fying as Epiphytacca;. Once I freed by violence Schizo- 
nema GreviUei and a Synedra which accompanied it, and 
they both moved about in a rather lively manner, although 
the motion of the Schizonema -was much more vigorous than 
that of the Synedra. This was not remarkable, as the frus- 
tules of Schizonema and Homceocladia are well known to be 
freely movable within their investing tubes, although I do not 
remember to have seen the fact of their activity without that 
enclosure recorded. The observance of these facts of the mo- 
tion of the detached frustules of such well-known forms as Schi- 
zonema, Gomphonema and Achnanthes, calls up in the mind the 
question of the individuality of the Diatomaceous frustule, 
and it is a point to which I would call the attention of 
students as one deserving and, in fact, calling for further 
and searching investigation. If the whole frond of a Homceo- 
cladia with its myriads of enclosed frustules is an individual, 
then is the usually free Nitzschia, a single frustule of which 
cannot be morphologically distinguished from a single de- 
tached frustule of Homceocladia, also an individual ? — and is a 
Navicula an individual as well as the group of similar forms 
enclosed within the tube of a Schizonema or the gelatinous 
frond of a Mastogloia ? Again, is a Cyclotella an individual as 
well as the long chain of discs which go to make up the frond 
of a Melosira or Podosira ? Upon this point I shall, hereafter, 
have more to say, merely begging the record of an observed 
fact bearing thereon by students of this extremely interesting 
and, I am convinced, important branch of natural history. 
VOL. IX. — NEW SEll. E 
