104 



Coelentera. 



network, occasionally giving rise to several stems, the colonies may 

 be closely attached to the substratum. 



On account of the feeble skeleton (cuticle) the colonies are 

 frequently supported by various bodies occurring in the water, 

 winding round or creeping over them. 



Very frequently the polyps of one colony are not all alike; for 

 instance, those persons which bear the medusa-buds are often 

 somewhat different from the rest, having smaller tentacles or none 



Fig. 60. IHydroid colony (Syncoryne fructicosa). Natural size. 2 two polyps of 

 tlie same, one with medusoid bnds, one of which is about to break free. 3 larva of another 

 liydroid (CordylopJiora lacustris). 4 — 6 the same after attachment. — After AUman. 



at all, or even possessing no mouth: in this case the cuticle 

 covers the whole body, and certain individuals (nutritive polyps), 

 which do n 1 produce such buds, perform the function of nutrition 

 for the whole colony. 



In some Hydroids there is yet a tlih-d kind of individual, thin, moutHess, 

 and very short, and bearing tentacles provided with a ^reat number of thread- 



