198 THE EVOLUTION OF SEX. 



In the tunicates the asexual process has again full play. It is not 

 confined to the passive sessile forms, where one might expect it, but occurs 

 in some of the free-swimmers as well. From a creeping stem buds may 

 arise, like plants from a rhizome ; or a parent form may bud oft" all round, 

 and finally die away, leaving the offspring in a circle round a cavity. Both 

 by budding and division chains may be formed, as in the salpas. In these 

 lowly vertebrates asexual multiplication terminates. How the process 

 often alternates in regular rhythm with ordinary sexual reproduction will 

 be discussed in the next chapter. 



