130 SKETCH OF THE INFUSORIA 



Upon these statements of Mr. Dalrymple, I venture to offer 

 the following remarks. 



1st. 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 fiexibilitij of the covering of many of 

 the C/osteria, which I have often noticed as wholly unlike the 

 brittle siliceous coverings of the Naviculae, and the fact that I 

 have never found their coverings among the fossil Navicular, 

 although the living species of each genus occur abundantly 

 together, all induce me to think the carapace of Closterium can 

 scarcely be siliceous. 



2d. Motions apparently voluntary. — These 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 chang- 

 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 a 

 portion of mud, covered with Closteria, is placed in a glass of 

 water, 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 in distinct cavities. — These 

 are easily seen ; generally there is one such cavity in each ex- 

 tremity, as indicated in most of our figures of Closterium, (see 

 figs. 30 to 38, PI. I,) but sometimes there are many such cavities ; 

 at other times almost the whole interior appears filled with active 

 molecules, as has akeady been stated (p. 123) is sometimes the 

 case with Euastrum. In specimens where the cavities at the 

 ends were very distinct, and which also showed very distinctly 

 the circulation referred to by Mr. Dalrymple, I noticed that the 

 form of the cavity containing the active molecules was constant- 

 ly changing, being sometimes globular, then elongating to the 

 left or right, and then becoming globular again, in a rapid but 

 very irregular manner. 



