COiLENTERATA. I59 



tive functions. In many the reproductive polyps are 

 so much reduced that they appear to be only organs, 

 and not individuals of a colony ; they were named 

 blastostyles (reproductive buds) or gonophores 

 (carriers of the reproductive organs) before their 

 morphological value as separate individuals was fully 



Fij. 36 — Blastostyles, b, of a colony of hydroid polyps; r, hydroirt 

 polyps retracted, e, expanded; c, enteron or digestive cavity, seen in optical 

 Bection. (Magnified.) 



recognised. The fully-formed medusa is to be re- 

 garded as a highly differentiated form of polyp, which 

 is often flattened out and largely modified with a view 

 to the necessities of a free-swimming existence. It 

 will be noticed that the medusa> compared with the 



