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NATURAL HISTORY. 



ORDER HYDROCORALLINA. 



The hard, stony, coral-looking substances dotted over with minute pores, and having, within, a 

 tubular structure crossed by platforms or tabulae, are called Millepores. They are reef-builders, and 

 contribute to the solidity of the coral reef structure, dwelling, however, in the warmest waters of the 

 tropics. Formerly classified with the true Corals, they are now, owing to the researches of L. Agassiz 

 and Prof. H. N. Moseley, placed among the Hydroids. The last-named and distinguished naturalist, 

 after having carefully examined the anatomy and development of the Millepores, during the 



expedition of H.M.S. Challenger, classified them in 

 association with certain deep-sea calcareous skeletoned 

 animals, called Stylasters, in a sub-order the Hydro- 

 corallinae. 



This is characterised by the presence of a calcai-eous 

 base made up of channels formed by the ectodermal part 

 of canals within them. The base is covered with a 

 continuous layer of derm, from which zooids of two forms 

 arise : one with a mouth and gastric cavity a gastro- 

 zooid ; * the other with tentacles and no mouth a dacty- 

 lozooid ; t they are retractible and lodge in the pores or 

 outer-chambers of the hard part. 



FAMILY MILLEPORID^E (WITHOUT AMPULLJE). 



The species of the genus Millepora are found on 

 Coral reefs, and the dense white substance forming their 

 usually visible portion is of stony hardness, and is marked 

 with numerous pore-like openings, small and sometimes 

 arranged in groups. A dried piece looks worm-eaten on 

 the surface around and between the pores, and these 

 lead down to long tubular cavities, across which flat layers 

 of the same mineral, carbonate of lime, which forms the 

 hard substance, generally stretch one over the other. 

 These are called tabulae, and they separate chambers, the 

 upper one being free above and open on the surface, and its floor is the last-made tabula. Between 

 the pores and their downward tubular prolongations is a curious hard structure made up of a network 

 of hard tissue, which gives the porous or worm-eaten appearance to the outside. Louis Agassiz and 

 H. N. Moseley both have discovered and described the soft parts on and within this dense white 

 substance, which much resembles, but is not, white Coral. A thin living film covers the whole 

 surface, and a thin downy layer is observed over all, and it consists of minute feeler-like projections 

 arising from the pores. Arranged as these pores are more or less in circlets around a central one, their 

 tentacles differ. The central larger one has a short body provided with a mouth, and it is a 

 cylindrical growth with from four to six short tentacles in one whorl at its top, just below the mouth. 

 Each of these tentacles has a knob at its tip, composed of nematocysts. The small mouth opening is 

 circular in outline, and a little lower down is a cruciform slit environed with gastric cells, bladder- 

 like and transparent. The other bodies surrounding this one, and coming forth from the circlet of 

 pores, are long and slender, cylindrical and tapering. They bear tentacles at regular intervals from 

 top to bottom, each of which consists of a short cylindrical stem with a knob. 



No mouth or stomach exists in these long bodies, and their office appears to be to catch food and 

 convey it to the short body with a stomach, in the middle of the circle. All disappear on very slight 

 shaking of the hard mass. The network of the hai-d substance, supporting these structures, contains 

 soft pai'ts and numerous tortuous canals, and some of these are on the surface and connect the 

 pores together. The hard structure, composed of fibrous-looking carbonate of lime, is produced by 

 the outer skin or ectoderm of the animal, and is nourished by and formed from the digested food, 

 which contains more or less carbonate of lime. 



* Greek, gaster, stomach. t Greek, daktylos, finger ; zoon, animal. 



CARMARINA (GERYOXIA) HASTATA. (ONE OF 

 THE TUACHOMEDU&E.) 



