76 CLASSIFICATIONS OF ZOOPHYTES. 



the mouth encircled with roug-hish filiform tentacula ; stomach with- 

 out proper parietes ; intestine ; anus ; rei^roductive gemmules 

 pullulating- from the body and naked, or contained in external vesi- 

 cles. Poli/pidcms horny, fistular, more or less phytoidal, fixed, ex- 

 ternal. Marine, excepting Hydra., which is lacustrine. 



Order II. Asteroida. Polypes compound, the mouth encircled 

 with 8 fringed tentacula; stomach membranous, with dependant 

 vasculiform appendag-es ; intestine ; anus ; reproductive gem- 

 mules produced interiorly. Polype-mass variable in form, free or 

 permanently attached, carnose, generally strengthened with a horny 

 or calcareous axis enveloped with the gelatinous or creto-gelatinous 

 crust in which the polype-cells are immersed, and which open on the 

 surface in a starred fashion with eight rays. Marine. 



Order III. Helianthoida. Polypes single, free or permanently 

 attached, fleshy, naked or encrusted with a calcareous Polypidom, 

 the upper surface of which is crossed with radiating lamellae ; mouth 

 encircled with tubulous tentacula ; stomach membranous, plaited ; 

 intestine ; anus ; oviparous, the ovaries internal. Marine. 



Sub-Class II. MOLLUSCAN ZOOPHYTES. 



Pody non-contractile, and nan- symmetrical ; mouth and anus 

 separate ; gemmiparous and oviparous. 



Order IV. Ascidioida. Polypes aggregate, the mouth encircled 

 with filiform ciliated retractile tentacula ; a distinct stomach, with 

 a curved intestine terminating in an anus near the mouth ; ova in- 

 ternal. Polypidoms very variable, — either horny, fistular and con- 

 fervoid, or calcareous, membranous, or fibro-gelatinous, formed of 

 cells connected and arranged in a determinate and usually quin- 

 cuncial manner. Marine and lacustrine. 



Additional Note. 

 The only extensive series of experiments we have on the composition of 

 Polypidoms are those of Mr Hatchett, published in the Philosophical Transac- 

 tions for 1800, and the subsequent progress of zoological and chemical science 

 requires a new investigation of the subject. The general results of Mr Hatch- 

 ett's experiments are, " that the Madrepores and Millepores are formed of a ge- 

 latinous or membranaceous substance, hardened by carbonate of lime, the differ- 

 ence consisting only in the mode in which these materials are combined : that 

 in the Tubipora, Flustra and Corallina, some phosphate of lime is mixed with 

 the carbonate of lime : that in the Isis the basis is a regularly organized mem- 

 branaceous, cartilaginous and horny substance, hardened by carbonate of lime, 

 one species only (the Isis ochracea) yielding also a small proportion of phos- 

 phate of lime. That the hardening substance of the Gorgonia nobUis is like- 

 wise the carbonate of lime, with a small portion of phosphate ; but that the 

 matter forming the membranaceous basis consists of two parts, the interior being 



