VORTICELLA. 



21 



d. It soon loses its peristome and disc, and assumes 

 the form shown in Fig. 11, the end which now carries 

 cilia being that which was attached to the stem. 



FIGS. 6, 7, 8, 9, 10, 11, and 12. 



FIGS. 6-12. Multiplication of Vorticella nebulifera. (Slightly altered 

 from Everts. ) 



FIGS. 6, 7, 8, 9. Stages in the process of multiplication by fission. 

 FIGS. 10, 11. The formation of a free individual. 

 FIG. 12. The process of conjugation. 



III. The Process of Conjugation. 



a. After swimming about for a time, it fastens itself, 

 by what was originally its upper or peristomal end, to the 

 side of the body of one of the ordinary fixed animals. 



b. The two then gradually become fused into one body, 

 as shown in Fig. 12. This process is essentially a process 

 of sexual reproduction, in which the entire bodies of the 

 two conjugating animals correspond to the two reproduct- 

 ive elements of one of the higher animals or plants. The 

 compound body formed by their union corresponds to a 

 fertilized egg or seed ; and it soon begins to multiply 

 again by division, although the precise method in which 

 division takes place, after conjugation, varies greatly in 

 different species of Vorticellidre. 



IV. Specimens may sometimes be found which have 



