No. 3-] MORPHOLOGY OF THE STENTORS. 527 



from the less specialized. Thus, in Stentor, the membranellae 

 are developed from the indifferent endoplasm, and in a place 

 remote from their final position. 



D. Conjugation. 



My observations on the conjugation of Stentor are very 

 fragmentary, for I have been unable to obtain sufficient 

 material for a complete study of it. Conjugation in all 

 species of Stentor is apparently a rare event. It was observed 

 by Stein ('67, p. 217) in 5. niger only ; by Moxon ('69) in 5. 

 cceruleus; and by Balbiani ('61, '82, '92), who has been the only 

 one heretofore to make any study of the nuclear phenomena 

 of the process, in 5. ccEriileus and vS. roeselii. I have found a 

 few conjugated individuals of S. ccendeiis and 5. igneus. In 

 spite of the fact that I h^"\^ had many large colonies of the 

 Blue Stentor for periods varying from two weeks to four 

 months, I have never observed an "epidemic" of conjuga- 

 tion such as Balbiani ('82, p. 161) says he has seen repeatedly 

 in case of vS. ccBndeiis and ^. roeselii. 



External PJienomena. — The only conjugates of .S. cceruleus 

 that I have obtained were found May 12-15, 1891, in a small, 

 ill-fed colony that had been in the laboratory for ten days. 

 Every individual in the colony was examined repeatedly during 

 the four days that conjugation prevailed, but out of two or 

 three hundred Stentors only fifteen couples were found. 



The Stentors in the culture were nearly all medium-sized 

 or small, and^^.as food was scarce, were very free from food- 

 vacuoles^.^ Usually the gametes were unequal ^ in size — in 

 one^,-instance very strikingly so (Fig. 50, PI. XXVI.). The 

 mode of attachment I have found to be exactly as it was long 

 ago described by Balbiani ('61), implicating only a small area in 

 the left-hand portions of the frontal fields of the gametes, and 

 thus compelling them to face in opposite directions, as it were. 

 The line of suture appears as a dense, glistening vertical band 

 (Fig. 49), and sections show that it is not merely a superficial 

 line, but a plate covering the whole surface of contact, and 



1 Out of the 1 5 pairs, the gametes of 9 were notably unequal in size. 



