58 SYNOPTIC COLLECTION. 



cilia next appears at the posterior end of the body of one 

 of the zoons (fig. 23), the forward end contracts, the disc 

 and cilia are drawn in (fig. 24), and finally by strong 

 efforts the zoon frees itself (fig. 25). The remaining 

 zoon afterward becomes free in a similar manner. The 

 movements of the free Vorticella are lively for a time, 

 then it becomes quiet, takes on a spherical form (figs. 26, 

 27), the wreath disappears and the nucleus divides (fig. 

 28). The shrunken cyst covering is seen in fig. 29 with 

 seven balls within. This completes the life cycle. This 

 species also increases through conjugation, as has been 

 stated. A smaller zoon, the microgonidium, approaches a 

 larger stemmed zoon, the macrogonidium (fig. 30). The 

 basal part becomes drawn in to form the sucker by means 

 of which the small zoon attaches itself to the side of the 

 larger one (fig. 31). When this is done, the conical base 

 is stretched out again, whereby a boring organ is pro- 

 duced, and the body of the small Vorticella becomes a 

 mere lump (fig. 32). Gradually the contents of the body 

 pass wholly into the larger zoon, leaving only a sac-like 

 skin (fig. 33). The bristles on this sac may be the wrin- 

 kles of the ring-like cuticle. Finally the sac-like skin is 

 thrown off (fig. 34), and the two animals are fused 

 together indistinguishably. It would seem that here the 

 whole body of the zoon corresponds to the ovum and the 

 spermatozoon, and if so, We have as the result of their 

 union a fertilized egg. Much difference of opinion exists, 

 however, in regard to the real significance of the act of 

 conjugation. But whether this act is a sexual or an asex- 

 ual one, it can be said with certainty that the process is 

 far more specialized than the apparently accidental fusion 

 of the Rhizopods. Furthermore, it. is rational to suppose, 

 as before stated, that this process is at least the initiatory 

 leading to the complicated reproductive phenomena of the 

 specialized Metazoa. l 



1 For a discussion of this subject, see Calkins, The Protozoa, 

 1901, chapter VII. 



