Mr. H. J. Carter on the Stromatoporidee. 309 



the polyp ; and this animal has but one opening, through 

 which the food is taken in and the refuse discharged. After 

 this a plurality of polyps are developed from stoloniferous buds 

 around the original one, in the form of a layer supported by 

 their calcareous coenenchyma, the original polyp developing 

 another polyp directly over itself; then other layers of 

 polyps accompanied by their coenenchyma follow, until the 

 ultimate form of the coral, whether branched or massive, is 

 attained; while as each layer of polyps is formed respec- 

 tively over its predecessor (increased by branching^ of course, to 

 fill up the extending circumference) the parts below pass into 

 coenosarc, whicli thus, for a time, fills up the interspaces of the 

 coenenchyma, until, in the massive corals, the. coenosarc itself 

 perishes, and thus the base becomes virtually dead. In 

 Madrepora abrotanoides the successive development of the 

 central or original polyps over each other is distinctly shown 

 by a branch which is broken off at each end, when the centre 

 of the coenenchyma at both extremities presents the septate 

 or mesentericated cell of the polyp, with this difference only, 

 that the structure is thicker or more condensed in the lower or 

 older part. Still the mesentericated tube is continued through- 

 out ; and as the corallum of the Hydrozoa is subject to the 

 same repetitionary conditions in development, it is not uncom- 

 mon to see the same tube, whatever this may have been, con- 

 tinued vertically through the mass in a similar growth of 

 Btromatojpora^ until it appears in the centre of the stelliform 

 hydrophyton on the surface, presenting the same appearance 

 over each successive layer of the coral. To this point I shall 

 have to return by-and-by, merely observing now that what 

 produces the polyp also produces the hydro})hyton, and there- 

 fore the two may have been combined or separate in the same 

 mass. 



A sponge, on the other hand, grows from an embryo which 

 develops a sarcoid surface-membrane pierced with holes 

 (pores) whicli are ever opening and closing, and interiorly 

 charged with hollow globular groups of mono-flagellated 

 animals, viz. the spongozoa. These, again, receive their food 

 through the pores, and discharge the refuse through the radi- 

 cles of a branched excretory canal-system, which, becoming 

 larger in proportion to the number of branches it receives, at 

 length terminates in an expanded vent or oscule on the sur- 

 face. Pari passu with this development, a skeletal structure 

 is formed, which, for the most part, is kerato-siliceous or 

 kerato-calcareous ; that is, it is composed of chitinous or 

 horny fibre strengthened by siliceous or calcareous spicules. 

 After this, the structure goes on increasing in bulk until the 



