A COLLFXTION OF HYDROIDS. 



307 



Trophosome. — Hydrorliiza is a creeping stolon, irregularly 

 branched. Diameter 0"152 mm., thickness of perisarc 18 /x. 



Hydrocaulus. — Simple upright stems irregularly divided 

 into hydranth-bearing and non hydranth-bearing internodes 

 by transverse and oblique nodes. The base of the stem is pro- 

 vided with two spiral turns. The apex of a stem is capable 

 of continued growth, and it may prodvtce a stolon-like out- 

 growth, indistinguishable from the hydrorhiza, from which 

 upright stems arise (text-fig. 8, C, O.IL). When the apex of 



Text-fig. 8. 



Cx3. 



Sertularia loculosa Husk. 



a stem comes into contact with a piece of weed or other 

 object, it appears to be stimulated to grow in this way, as 

 separate pieces of weed may be firmly bound together by 

 outgrowths of the ends of the stems. 



Length of hydranth-bearing internode, measured from a 

 transverse joint to the opposite pointed extremity of an oblique 

 articulation 0"50 nan. 



Hydrotheca. — Short and broad, opposite; in contact in 

 front (Z>), separate behind (D). Horizontal fold occurs about 



