SIX-RAYED POLYPS 3483 



surrounded by its crown of tentacles. These madrepores play no small part 

 in building up coral reefs, and the many different elegant forms which they 

 assume (while keeping to their method of budding) is astounding. Some 

 corals, again, do not form true branches, but may cover the ground like 

 a field of corn, a good example of this type being found in Cladocora c&spitosa, 

 which inhabits the Mediterranean and Adriatic seas. Here the single indi- 

 viduals form somewhat long tubes, and the buds arise laterally at the lower end, 

 then bend upward and grow alongside of the parent, without any further connec- 

 tion or fusion. The spaces between the different rising polyps are not filled in 

 with secreted hard matter, but the latter grow up side by side free. The 

 stock, therefore, is easily broken. This coral flourishes extraordinarily in many 

 places, covering areas of over one hundred square yards, with a growth of a foot in 

 height. 



The method of growth just described is shown also by another and quite differ- 

 ent coral, Astroides calycularis. As in Cladocora, just described, the single polyps, 



DEVELOPMENTAL STAGES OF Astroides calycularis, 

 (Magnified 24 times.) 



with their calcareous tubes or pedestals, are not fused together by any cementing 

 substance. The yellowish-red polyps are seen standing out a great height above 

 their cavities, much more so than is usual in corals. The larvae of these corals 

 leave the egg while still in the large, chambered body cavity of the parent, where 

 they swim about for a time, till they escape through the mouth. They are long and 

 worm-like, and slightly thicker at the posterior end, but may change considerably 

 in shape. They swim about rapidly by means of their covering of cilia, the thicker 

 end being foremost. The mouth appears at the thinner end soon after the larva 

 leaves the body of the parent. Its free-swimming life has been known to last as 

 long as two months; but under natural conditions it would probably be shorter. A 

 strong sirocco had a marked effect upon the larvae, which seemed to become ex- 

 hausted, contracted, and became attached. The transition from the worm-like 

 larva to the polyp takes place as in the anemones. The thicker end of the body is 

 pressed against a hard rock, and the whole contracts into a thick, round disc; while 



