218 ZOOLOGY 



forming colonies by budding, somewhat after the fashion 

 of plants. The other groups are the Bryozoa, or "sea- 

 mats," and the Timicata, or " sea-squirts." In all cases 

 the buds arise from a definite part of the parent body and 

 develop into a definite form, often exactly like that pro- 

 duced from the egg. When the buds remain attached to 

 the parent, a compound individual or colony is produced. 

 These colonies differ greatly in form. Thus among liy- 

 droids we have colonies which produce runners, from which 

 alone, and not from other hydranths, new hydranths arise. 



FIG. 205. Atoll in Fiji Islands (Nanuku Levu). The large circle of white 

 made by breakers indicates the position of the coral reef. A small bit of 

 land still remains in the interior lagoon. Photo, by Dr. W. McM. Wood- 

 worth. From A. Agassiz, " Coral Reefs of Fiji." 



In another case (Obelia), one hydroid buds from the side 

 of another and rises beyond it, continuing the main stem 

 of the colony. Since its descendants do the same, the stalk 

 is made up of successive generations of hydranths. Some- 

 times the hydranths are placed close together and oppo- 

 site, like the leaves of Arbor vitse (Sertularia, Fig. 197). 

 Again, there may be a main stalk composed of one hy- 

 dranth and a series of lateral branches in one plane, mak- 

 ing a fan-like arrangement of the colony. Or the lateral 

 branches may arise in any plane, producing a bushy colony. 



