488 



CCELENTERA TES. 



more than two kinds of individuals; namely, the nutritive individuals, dis- 

 tinguished by their long tentacles, mouths, and digestive cavities; and the 

 reproductive individuals, male or female. These latter have no mouths, and are 

 supplied with food through the system of canals running to them from the 

 nutritive individuals. These reproductive individuals, instead of tentacles, carry 



at their tips a -circle of stinging- 

 batteries for the protection of 

 their eggs, which are enclosed in 

 capsules clustered together round 

 the stalk a little way below the 

 tips. The ciliated larvse emerg- 

 ing from the eggs swim away, 

 and eventually become attached 

 and found new colonies. The 

 egg- capsules in no way recall 

 rnedusse, but all medusae which 

 pass through a polyp-like inter- 

 mediate stage also pass through 

 the simple capsule stage. 



Two more of the Hydroid 

 stocks are worth mention, since 

 they secrete masses of carbonate 

 of lime out of which the animals 

 protrude like corals, which indeed 

 they were thought to be. This 

 error was made because only the 

 massive skeletons of the Hydro- 

 corallia as they are called and 

 not the living animals were 

 known. Instead of the horny, 

 often delicately branching in- 

 tegumentary skeleton usually 

 found in the Hydroid polyp 

 stock, that of the Hydrocorallia 

 contains ninety-seven per cent, 

 of carbonate of lime, and forms 

 rough, solid-looking masses, with 

 lobed processes or bosses like 

 those figured on p. 490, or else 

 (Stylasteridce) branches, like the precious coral of commerce. The whole surface 

 can be seen even with the naked eye, but still better with a lens, to be covered 

 with small pore-like apertures. Closer examination shows that these are of two 

 sizes, a larger central pore being surrounded by an irregular circle of from five 

 to eight smaller ones. The mass of the colony is traversed by an irregular 

 system of numerous branching canals of different sizes. In vertical section, 

 indistinct layers can be seen running almost parallel with the outer surface. 



GROUP OF A FEMALE STOCK OF Hydractinia echinata. 

 a, Nutritive individuals ; b, Female individuals. (Enlarged. ) 



