140 DESCRIPTION OF [Polygaslrica. 



a little distance behind one extremity proceed two bristles, 

 or tentacula, of excessive tenuity, which the animalcule 

 incessantly agitates with great rapidity. These are pro- 

 bably organs of locomotion, similar to the filiform prolon- 

 gation, found in the Infusoria without cilia. Indeed, the 

 part thus furnished with tentacula moves foremost, 

 drawing after it the rest of the body, which turns about 

 in the water, but always preserves its turriculate form. 

 The incessant agitation of these tentacula, and their ex- 

 treme tenuity, rendered it impossible to observe them in 

 the living animal; recourse was therefore had to the 

 evaporation of the water, or to the application of a slight 

 tincture of iodine, when the animalcules ceased their 

 motions, became contracted, and their spiral unrolled, when 

 the tentacula were rendered very distinct, from their brown 

 colour. These tentacula were frequently observed to be 

 soldered together, from one-half to one-third of their 

 length upwards, but others were also noticed to be 

 entirely separated down to their bases. A swelling similar 

 to that in the flexure of the body was perceived in their 

 curves. 



" Ammonia arrested their motions, and contracted the 

 body gradually into a small oval mass, but did not pro- 

 duce the phenomenon of decomposition by solution 

 (diffluence], so remarkable in the Infusoria. A very weak 

 solution of chlorhydric acid in water violently contracted 

 them into a shapeless mass/' 



In plate xii.,^. 519, 520, and 521, represent the sperma- 

 tozoa found in Polytrichum commune, the first figure exhi- 

 biting them enclosed in the cellules, and the others swim- 

 ming freely. Figures 522 to 524, are taken from Marchantia 



