90 



HTDKOZOA. 



The entire order is sometimes denominated 

 Tubularidce , and agrees with the group Tubu- 

 larina of Ehrenberg. 



4. Order 3 : Sertularidae. — Like the mem- 

 bers of the preceding order, all the Sertularidw 

 after the expiration of their embryonic condition 

 become permanently fixed by means of the hydro- 

 rhiza which forms the proximal extremity of the 



1 



{fig 



In this group the tendency 



to increase by gemmation is even greater than 

 among the Corynidce, for no example of a Sertu- 

 larid has yet been recorded in which the hydro- 

 soma exhibits but a single polypite. The coenosarc 

 is plant-like and, frequently, m uch branched, the 

 main stem either losing itself in its own ramifica- 

 tions or remaining distinct throughout the entire 

 length of the arborescent mass. A good example 

 of the latter mode of growth is afforded by the 

 Sea-Fir, Sertularia cupressina, the hydrosoma 

 of which may attain a height of two, or even three, 

 feet, and bear on its branches so many as 100,000 

 distinct polypites. In contrast with this, the 



oned 



the delicate Sertularia ienella, the length of whose 

 slender creeping hydrosoma scarcely reaches one 

 inch. The waving fronds of Oar-weed on various 

 parts of the coast afford a suitable habitat to the 

 anastomosing thread-like coenosarc of another char- 

 acteristic species, Campanularia genicu lata, which 

 sends up at intervals its peculiar zig-zag branches, 

 from the angles of which the polypite stalks 

 arise. Other S&rtularidce attach themselves to 

 stones or shells, and not a few of the smaller forms 

 occur parasitically on the stems of more conspic- 



largest ^ of our native species, may be menti 





c 



1 



t 



( 



1 



5 



