REPRODUCTION. 



lOI 



not detached from, the organism which gave it birth. This 

 is an instance of what is called " continuous gemmation." 



In other cases — as in the common fresh-water polype or 

 Hydra (fig. 8) — the buds which are thrown out by the 

 primitive organism become developed into creatures exactly 

 resembling the parent; but, instead of remaining permanently 

 attached, and thus giving rise to a compound organism, they 

 are detached, to lead an entirely independent existence. 

 This is a simple instance of what is termed " discontinuous 

 gemmation." 



The method and results of fission may be regarded as 

 essentially the same as in the case of gemmation. The 

 products of the division of the body of the prinjitive organ- 

 ism may either remain undetached, when they will give rise 

 to a composite structure (as in many corals), or they may 

 be thrown off and lead an independent existence (as in some 

 of the Hydrozoa). 



An excellent example of simple discontinuous fission is 



;/--i 



V-" 



Fig. 28. — A, Pnrainoccinm, showing the nucleus (w) and two contractile vesicles (r) 

 B, ParaitKrcivyn bursaria (:K{\.xir Stein), dividing transversely: « Nucleus; «' 

 Nucleolus ; 7' Contractile vesicle. C, Paratnoccmm aurelia (after Ehrenberg), 

 dividing longitudinally. 



afforded by the common animalcule, Paramecium (fig. 28). 

 This litde creature produces fresh beings by a process of 



