BEYOZOANS. 105 



S. P. Sharpies found the coral of M. alcicomis to consist 

 of 97*46 per cent of carbonate of lime, 0*27 of phosphate of 

 lime, and 2*54 of water and organic matters. The Millepores 

 are very abundant corals, and eminently so in the West In- 

 dia seas, contributing largely to the material of the reefs. 



The Hydroids were long considered polyps. But they 

 have been found to give origin to Medusas or jelly-fishes, and 

 it is now proved that they are only an intermediate stage in 

 the development of Medusae, between the embryo state and 

 that of the adult or Medusa state. The Millepores afford, there- 

 fore, examples of coral-making by species of the class of Aca- 

 lephs. Many of these Medusae and their Hydroids will be 

 found illustrated in the admirable work of Alexander and Mrs. 

 L. Agassiz entitled " Sea-Side Studies " — an excellent com- 

 panion for all who take pleasure in sea-shore rambles. 



Another genus of corals referred to the Millepora group 

 occurs in the East Indies, the species of which is remarkable 

 for having within an indigo-blue color ; it is called Heliopora 

 caerulea, the generic name, from the Greek for sun, alluding to 

 the minute round polyp-cells. This and the true Milleporaa, 

 are coral-reef species. A few allied species occur in colder 

 waters, and for these the genus Pliobothrus has been instituted ; 

 one species has been described by de Pourtales, from the deep 

 waters off the Florida reef. The ancient corals of the Chas- 

 tetes family were probably like the Millepores in being Aca- 

 leph corals, as suggested by Agassiz. 



IH BRYOZOANS. 



The Bryozoans are very small animals, and look much like 

 Hydroids. Although belonging to the sub-kingdom of Mol- 

 lusks, they are externally polyp-like, having a circle or ellipse of 



