90 HTDROZOA. 



The entire order is sometimes denominated 

 Tubularidcc, and agrees with the group Tubu- 

 larina of Ehrenberg. 



4. Order 3 : §ertularidap. — Like the mem- 

 bers of the preceding order, all the Sertularidce, 

 after the expiration of their embryonic condition, 

 become permanently fixed by means of the hydro- 

 rhiza which forms the proximal extremity of the 

 coenosarc {fg. 4, c). In this group the tendency 

 to increase by gemmation is even greater than 

 among the Gorynidce, 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, much 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, Sertidaria cupresslna, 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 

 largest of our native species, may be mentioned 

 the delicate Sertularia tenella, 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, Gampanularia geniculata fVfhich 

 sends up at intervals its peculiar zig-zag branches, 

 from the angles of which the polypite stalks 

 arise. Other Sertularidce attach themselves to 

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

 occur parasitically on the stems of more conspic- 



