476 JOHNSON. [Vol. VIII. 



3. Stent or jveselii, Ehrbg. 

 (Fig. 4, PI. XXIII.) 



I find no essential difference between the American speci- 

 mens of this form and the European 5". roeselii so admirably 

 figured by Stein ("67, Taf. VII, VIII). The meganucleus is 

 often moniliform, it is true (Fig. 4, vtgn.), but this condition 

 has been found to obtain in the European form as well. 



5. roeselii, like all its genus, is variable in size and shape. 

 Specimens from Alewife Brook, Cambridge, are for the most 

 part very small; while those found at Williamstown were 

 unusually large, measuring when fully extended, 2 mm. in 

 length and .19 mm. across the expanded frontal field. 



This species frequents quiet waters where flocculent vege- 

 table debris abounds, in the midst of which the so-called 

 "sheath" is formed (Fig. 4, j-//.). It is generally held that 

 the sheath is due to a mucilaginous secretion. After observing 

 carefully the habits of the animal, its surroundings, and the 

 structure of the sheath, I am strongly inclined to the view 

 that there is no secretion, but that the sheath is made up 

 wholly of the slime and bacterial zoogloea in the midst of which 

 this Stentor delights to anchor itself. As I have observed it, 

 the sheath is of the most indefinite form, and indistinguishable 

 from the surrounding slime. As Stein long ago pointed out, 

 the sheath has imbedded in its substance various minute foreign 

 bodies (bacteria, diatoms, etc.), the presence of which is not 

 favorable to the view that the sheath is secreted by the animal. 



Although 5. roeselii is perhaps the most sedentary of its 

 genus, it is often seen swimming, when it assumes a clavate 

 form, but slightly widened at the anterior end. On attaching 

 itself, it expands into a graceful trumpet- or calla-like form 

 (Fig. 4). In this condition 5. roeselii is readily distinguishable 

 from colorless specimens of 6". polymorpJiiis (the 5. Mulleri of 

 Ehrenberg) not only by its more slender form, but still more 

 sharply by the characteristic shape of the frontal field. In 

 fact, the frontal field of this species displays the highest 

 development of any Stentor, and judged by this character 

 alone, S. roeselii would rank the highest of the Stentors. 



