SPONGES, ZOOPHYTES, AND SEA-FIRS. 45 



the commonest naked zoophytes ; for such detailed descrip- 

 tion as may render the recognition of actual specimens 

 possible, reference should be made to the tables at the 

 end of the chapter. 



In Hydractinia we have already described a zoophyte in 

 which the skeleton is very slightly developed, but there is 

 another pretty form in which there is even less horny 

 matter. This is the club-shaped zoophyte ( Clava squamata), 

 often exceedingly common between tide-marks. If in shore 

 collecting you are endeavouring to throw back the heavy 

 dripping curtains of bladder- wrack, which hang pendent in 

 front of the great rock-clefts, you may often notice little 

 pink fleshy spots on the weed. In- 

 significant enough they look, but it 

 is well worth your while to break off 

 a bit of the weed and drop it in a 

 clear pool. You will then find that 

 the fleshy mass is a dense cluster of 

 short stout zooids, which soon un- 

 fold in water and display their 

 characteristic club-shape (see Fig. 

 13). Each bears numerous scattered 

 thread-like tentacles, and at times, 

 in addition to these tentacles, one 

 finds that the zooids have a distinct FIG. is. ciava squamata on 

 collar made up of little beads. These weed - After oilman, 

 are clearly shown in the figure. Each bead is a sporosac, 

 containing eggs, which grow directly into fresh colonies. 

 The individuals may reach a length of about an inch, but 

 the colonies never contain very many individuals. There is 

 no skeleton save a slight attaching plate on the weed. 



As the next stage in the development of skeleton we 

 may mention Hydractinia where we have the spines in 

 addition to the basal plate. It is also remarkable because 

 of the fact that, as already mentioned, the colony includes 

 three different kinds of individuals. This " polymorphism," 

 or occurrence of more than one form, is rare among the 

 Hydrozoa of the shore, though it commonly occurs among 

 those of the open sea, e.g. in the "Portuguese man-of-war" 

 of the South Coast. 



In the next zoophyte to be mentioned we find that the 



