308 GEORGE W. TANNREUTHEK. 



CONJUGATION. 



Conjugation occurs shortly after the animals escape from the 

 cysts. In the early stages of conjugation the conjugants become 

 spherical and press closely against each other, giving the sem- 

 blance of binary fission. The animals rotate very rapidly on 

 their long axes, slightly moving back and forth on the sides in 

 contact (Fig. ja). The anterior ends of the conjugants are 

 slightly turned towards each other, so that the free end of either 

 pharynx comes in contact. A small cytoplasmic bridge is then 

 formed between the two individuals in close proximity and in 

 front of either sub-terminal oral aperture. Thus the conjugation 

 is terminal or end conjugation instead of lateral which is more 

 common in the ciliates (Figs. 3, 8). The animals feed but little 

 during conjugation. The conjugants often vary considerable in 

 size. The period of conjugation lasts about four hours. When 

 the union of the two animals is complete they elongate, with 

 their anterior ends turned towards each other, and swim rapidly 

 through the water, rotating on their long axes (Fig. 3). This 

 method of activity may continue until conjugation is complete. 

 But the greater number of conjugants observed during the 

 process, became quiescent usually in contact with some sediment. 

 They assumed a spherical form and rotated quite rapidly. 

 While in this position a temporary cyst is often formed and the 

 conjugation is completed within the cyst (Fig. 26). If the cyst 

 however, with the conjugants is disturbed they may escape before 

 conjugation is complete and again move freely through the 

 culture. A second temporary cyst is seldomly formed. This 

 process of conjugation within a cyst is often taken for binary 

 fission and that the two daughter cells produced within the cyst 

 conjugated before escaping. This however, is not the case, since 

 the first steps in conjugation of all individuals, as observed under 

 the microscope, took place in the free swimming stage. The 

 temporary encystment of the conjugants when it occurs is second- 

 ary and not essential except in sudden adverse conditions, since 

 it does not occur in normal conditions if the forms are continually 

 agitated during conjugation. 



The relation of the conjugants in a straight line with their 

 anterior ends united as the figures indicate, is due more to their 



