210 



ZOOLOGY 



under the microscope each stem appears as a series of 

 hydranths placed in zigzag 1 fashion, one beyond the other. 



FIG. 10(!. Obelia ( ?) , a group of campanularian hydroid colonies. Nat. size. 



Photo, by W. H. C. P." 



Another common kind is Sertularia, 1 which forms rusty 

 brown threads (Fig. 197 ). All the hydranths of one stem 



occur in one plane and 

 oppositely. 



Both t u 1) 11 1 a r i a 11 and 

 c a m p a 11 u 1 a r i a 11 hy droids 

 may give rise to jelly-fishes. 

 These jelly-fishes are formed 

 as buds on the hydrant] i, and 

 after they become able to 



move of themselves they are 

 ;. 1<7. Sertularia, a small colony. J 



i.r> nat, size. cut off from the parent and 



1 Derived from serta, garland. 



