536 DESCRIPTION OF \J?olygasiricA. 



base. Close to the bottom of the oral sac lies a contractile vesicle, 

 and near this a larger finely granular spot, well defined, and higher 

 up than this again, a similar but smaller spot. The two latter spots 

 are the opposite extremities of the band-like nucleus, lying on one 

 side the mouth. 



The stem or pedicle is inflexible, and apparently hollowed inter- 

 nally by a canal ; the animals seated on its branches have considerable 

 latitude of motion by their mode of articulation ; and they also are 

 able, in some degree, to shorten themselves by the annular segments 

 of their base. 



Both animals and pedicles undergo spontaneous fission, which 

 happens just as in Vorticella ; however, the new forms produced, do 

 not, in Eimtijlis, develope posterior cilia, but progress by means of 

 theu' usual frontal apparatus. 



All the members of the same little-tree (polypidom) are of nearly 

 equal size; the largest noticed were l-20th. of a line in length ; 

 whilst in other polj-pidoms, whose stems and branches were propor- 

 tionately thinner, examples were met with of very minute size 

 (P. 22, f. 22, 23). In the smallest, no anterior cilia, and no 

 contained globules were visible ; in larger ones, though only 1-1 50th. 

 of a line in length (P. 22, f. 23) such were found. These latter 

 foiTns constitute the Epistylis Botrylis (Ehr.) 



Besides fission, Dr. Stein presumes Epistylh has another mode of 

 generation by metagenesis, wherein it is transformed into an acineta- 

 like individual, which again becomes the parent of ciliated vesicular 

 embryos. The change of an Epistylis into an Acineta has not been 

 actually witnessed, and neither is the farther history of the sub- 

 sequently developed, ciliated embryo cell, kno-wn. But Dr. Stein 

 rests his opinion chiefly upon an analogy with Vorticella and Vaginicola, 

 in which he has actually seen the transformation into Acinetm, and 

 also upon the similarity of the pedicle, and the movements of the 

 Acineta body upon it. 



The supposed Acineta of Epistylis nutans appears to have escaped 

 notice, although of common occurrence at all seasons of the year, 

 even under the ice, growing upon duckweed and other aquatic 

 plants (P. 22, f. 18). The normal shape of the Acineta is ovate or 

 pyrifurm (P. 22, f. 17, 18); but may be variously and greatly 



