ASEX UAL REP ROD UC TION. 



183 



other syllids, the separation of a series of joints as a sexual individual has been 

 repeatedly observed, or this may be reduced till only one joint, laden with 

 reproductive elements, is set free. In many of these chaetopods the budding 

 begins when the normal size of the individual has been stopped by unfavorable 

 conditions, which bring about separation, and the subsequent sexuality of the 

 liberated individuals. 



Fig. 60. — Adventitious buds forming at the sides of a leaf of 

 Bryophyllum calycinum. — From nature. 



Starfishes and the like surrender their "arms" so readily, that some have 

 supposed that they might, in this way, normally multiply. A voluntary 

 surrender of parts as a mode of multiplication is, however, in this case difficult 

 to prove. So while crustaceans, insects, spiders, and mollusks may lose and 

 regrow certain parts, no asexual multiplication occurs. 



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 off 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. 



