IV 



PHYLUM CCELENTERATA 



147 



branches are little cup-like projections, with radiating processes 

 passing from the wall of the cup towards the centre, and thus 

 closely resembling the true cup-corals belonging to the Actinozoa 

 (vide infra). But in the case of Stylaster each " cup " is 

 the locus, not of one, but of several zooids : a polyp projecting 

 from its centre, and a dactylozooid from each of the compartments 

 of its peripheral portion. 



The gonads of Millepora are formed in small capsules, occurring 

 in the course of the ccenosarcal canals ; in Stylaster there are 



B 



FIG. 105. Stylaster sanguineus. A, portion of skeleton, natural size ; B, small portion, 

 magnified ; a. ampullte ; d.j>. dactylopores ; ;/.^;. gastropores. (After Nicholson and Lydekker.) 



sporosacs or degraded reproductive zooids lodged in special cham- 

 bers () of the coral. 



The Hydrocorallina occur only in the tropical portions of the 

 Pacific and Indian Oceans, where they are found on the " coral 

 reefs " partly or entirely surrounding many of the islands in those 

 seas. Fossil forms are found as far back as the Triassic epoch. 



ORDER 4. SIPHONOPHORA. 



The diversity of form exhibited by the members of this order is 

 so great that anything like a general account of it would only be 

 confusing to the beginner, and the most satisfactory method of 

 presentation will be by the study of a few typical genera. 



Halistemmd (Fig. 10G A) occurs in the Mediterranean and other 



seas, and consists of a long, slender, floating stem, to which a 



number of structures, differing greatly in form, are attached. At one 



the uppermost end of the stem is an ovoid, bubble-like bodv con- 



L 2 ' 



