138 



THREE CRUISES OF THE " BLAKE.' 



HYDROCORALLIN.E. 



To the hydroids we should add the account of the Hydro- 

 corallinse, which until recently were supposed to be true corals. 

 Professor Agassiz, however, observed the animal of Millepora, 



and traced its acalephian affinity. 

 The polyps of Millepora are most 

 difficult to observe (Fig. 441), 

 not only on account of their small 

 size, but also from their extreme 

 sensitiveness to contact with air. 

 Agassiz's observations have been 

 confirmed by several investigators, 

 especially by Moseley, who has 

 greatly increased our knowledge 

 of the group, and has in addition 

 shown that other families of cor- 

 als, the StylasteridaB and Helio- 

 porida?, belong with the Millepo- 

 ridse to a natural group for which he has proposed the name 

 Hydrocorallina3. They are all characterized by having reproduc- 

 tive, prehensile, and digestive zoids composing the community 

 (Fig. 442), reminding us thus somewhat of the siphonophores. 



Fig. 441. Animal of Millepora. 



(Agassiz.) 



Fig. 442. Millepora nodosa, Dactylozoid Gastrozoid ; magnified. (Moseley.) 



The best known member of the group is the shallow-water 

 Millepora (Fig. 443), which is represented in deep water in the 

 Caribbean and Florida districts by Pliobothrus symmetricus. 



