300 Sketch of the Infusoria of the family Bacillaria. 
“The author therefore concluded that Closterium must-still be re- 
tained as an infusory animal, although it is more than doubtful whether 
it‘ought to rank with the polygastric families.” 
Upon the above statements of Mr. Dalrymple, 1 venture to 
offer the following remarks. 
Ist. As to the siliceous nature of the carapace: Ehrenberg ex- 
pressly states, (1. c. p. 446,) that “the carapace can be burned 
and completely volatilized.” This statement of Ehrenberg, to- 
gether with the undoubted fleribility of the covering of many of 
the Closteria, which I have often noticed as wholly unlike the 
brittle siliceous coverings of the Naviculz, and the fact that I 
have never found their coverings among the fossil Navicule, al- 
though the living species of each genus occur abundantly together, 
all induce me to think the iis of Closterium can ly 
be siliceous... 
2d. Motions apparently piatdiae-iteses are easily seen ; I 
have often’ been unable to sketch the form of a specimen by 
means of the camera lucida, as the body was constantly ehang- 
ing its position, and this too when certainly undisturbed by the 
motion of other animalcules or any extraneous cause. Their 
power of locomotion may also be rendered apparent thus: if @ 
portion of mud covered with Closteria is placed in a glass of wa 
ter, exposed to light, and the Closteria are then buried in the 
mud, they will soon work their way to the surface, covering it 
again with a green stratum which may be buried over and over 
again, with the same results. — 
_ 3d. Presence of moving molecules i in distinct cavities —T hese 
are easily scen; generally there is one such cavity in each ex 
tremity, as indicated in most of our figures of Closterium, (see figs. 
30 to 38,.Pl..1,) but sometimes there are many such cavities; a 
other times almost-the whole.interior appears filled with active 
molecules, as has already been stated (p. 296) is sometimes” 
case with Euastrum. In specimens where the cavities at the 
ends were very distinct, and which also showed very distinetly 
the circulation referred to by Mr. Dalrymple, I noticed that the 
form of the cavity containing the active molecules was constantly 
fan ¢ sing, being sometimes globular, then elongating to the 
3 and then “becoming globular again, in a rapid but very 
Sx : of distinct | et circulation. — This was ; noticed many 
years ago jo by Giruladeek “The account by Mr. Dalrymple, giv 
