324 JOURNAL OF SCIENCE, 
sion in a specimen of Cosmarium botrytis. The question whether 
the Desmidieze move “voluntarily” or not seems to have never 
been clearly settled. That they move towards the light, if in 
mud, has long been known, and some observers have mentioned 
motions in Clostevium, But others deny that the Desmids move 
voluntarily, and their travelling towards the light may be simply 
due to the stimulus of light, The term “voluntarily ” is here used 
in the same sense as when referring to Diatoms, which certainly 
travel in all sorts of directions. Some observers also have spoken 
of “cilia” and “ retractile processes” as noticeable in Desmids, 
but these also have been denied. In the case in question the 
Cosmarium was observed for about three hours, and in that time 
it travelled, without any external disturbing influence, backwards 
and forwards like a Diatom, steering round obstacles, advancing 
and retreating, rolling over and over, and generally behaving 
with quite as much “voluntary ” effort asa Diatom. The motion 
however, was not an easy, gliding, smooth motion, but a succes- 
sion of sharp jerks, pushing forward first one side and then the 
other, “ exactly like that of a man elbowing his way through a 
crowd.” On the whole, the author concluded that the Desmid 
might be said to travel quite as “voluntary” as any Diatom, 
But, with the most careful scrutiny, under various lights and con- 
ditions. not a trace could be made out of cilia or retractile pro- 
cesses, or of any effect on the surrounding water indicating them. 
There are also remarks upon a point in connection with the 
conjugation of Closteviwm acerosum and of Closterium seleneeum, Mas- 
kell. The process in the latter plant which was observed on one 
occasion up to the point of formation of the zygospores (when 
unluckily the specimen was crushed by an accident) resembles 
that in Closterium ehvenbergit, as described by the Rev. W. Smith, 
in the Ann. and Mag. of Nat. Hist., 1850, p. 1 and plate 1, and 
it is highly interesting. The conjugating fronds approach in 
pairs, surround themselves with a distinct mucous envelope, and 
then undergo division. From this it results that four fronds 
appear in the envelope, each having one long’and one very 
short segment; and the conjugation takes place between each 
adjacent pair of these new fronds, so that the process is double, 
and two zygospores are produced. Clostevium ehvenbergit has been 
hitherto supposed to be the only plant with this character, but 
(. seleneum has now to be added to it. The author also believes 
that C. acervoswum undergoes a process nearly similar, because in 
that plant, in conjugation, it is invariably observed that each 
frond has one long and one very short arm. This fact, although 
shown in all figures by different writers—Ralfs, Pritchard, Ehren- 
berg, &c.—is not alluded to by any in their descriptions. There 
seems to be only one way of accounting for it, namely by the 
self-division of the fronds before actual conjugation is effected. 
In a mass of conjugating fronds observed by the author, there 
was no instance of any in which the segments were of equal 
length. At the same time there was no distinct mucous envelope 
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