POLYPI. 



[ 524 ] 



POLYPODIES. 



hollow tentacles and the canals of the poly- 

 pidom. In the Bryozoa, the abdominal 

 cavity of which is closed from the digestive 

 cavity, the current runs continuously and 

 regularly in one direction ; whilst in the 

 Anthozoa, its direction varies according to 

 whether the Hquid passes from the abdominal 

 to the gastric cavity or from the latter to the 

 former. 



The propagation of the polypes takes 

 place in three ways : by spontaneous divi- 

 sion, which is mostly longitudinal and rare ; 

 by the formation of gemmae or buds, which 

 is very common, the individuals either sepa- 

 rating or remaining attached ; and by the 

 formation of ova. This probably takes place 

 in all polypes, and requires the presence of 

 a testis and ovary, which have been dis- 

 covered in several polypes. These organs, 

 or their representatives, are variously distri- 

 buted. In some, both are present in a single 

 individual {Hydra) ; whilst in others the 

 sexes are separate (Actinia). In the colonial 

 polypes the individuals are of distinct sexes, 

 both kinds occurring either upon the same 

 {Alcyonella), or upon distinct polypidoms 

 (Alcyonium, &c.). Some polypes are always 

 a-sexual, individuals of a totally dissimilar 

 form arising from them and their polypi- 

 doms by gemmation, in which sexual organs 

 are afterwards formed {Coryne, Campanu- 

 laria, &c.). In some, these individuals, 

 which are mostly bell- or disk-shaped, sepa- 

 rate from the polypidom before their sexual 

 organs have acquired full development, and 

 swim about like Acalephce, the mature deve- 

 lopment subsequently ensuing (some Cam- 

 panularice, &c.) ; in others, again, it takes 

 place while they remain attached. 



The bodies in which the gemmules or ova 

 are formed are usually called bulbules, ovi- 

 gerous vesicles, or ovisacs. 



The ova of the polypes are surrounded by 

 a more or less hard envelope, which in some 

 is simple, in others possessing a peculiar 

 structure, being covered with hooks, &c. 

 (PI. 33. fig. 10). 



The embryo of the polypes is usually 

 more or less elongate-oval, coated with cilia, 

 and moves about on its long axis like an 

 infusorium; after a short time it fixes itself 

 to some object, the cilia then disappear, and 

 the tentacles of the polypes are protruded. 

 Many of these polypes then increase by 

 gemmation, thus forming new colonies. 



The formation of coral-reefs and islands 

 by the skeletons of polypes is well known. 

 The class Polypi is divided thus : 



Ord. 1. Anthozoa. Body contractile, 

 symmetrical; a single external orifice only 

 to the alimentary cavity ; gemmiparous and 

 oviparous. 



Ord. 2. Bryozoa (Polyzoa). Body non» 

 contractile, unsymmetrical; alimentary canal 

 with an oral and anal orifice ; oviparous. 



BiBL. Johnston, British Zoophytes ; 

 Siebold, Vergl. Anat. 25; Wagner, Icones 

 Zootomicce ; Farre, Phil. Trans. 1837; v. 

 Beneden, Mem. s. les Campanulaires ; Vogt, 

 Zool. Brief e; Owen, Hunterian Lectures, i,; 

 Lister, Phil. Trans. 1834; Couch, Corn. 

 Fauna ; Hancock, Ann. Nat. Hist. 1850. v. 

 173; Desor, Ann. d. Sc. nat. 3 ser. xii. ; 

 Dana, Report on Zoophytes. 



POLYPOpiACEiE.— A family of Ferns, 

 divided into six tribes by the characters of the 

 sporanges. 



Synopsis of the tribes. 



I. PoLYPODiEvE. Sporanges numerous, 

 united in sori, and divided into two equal 

 parts by a vertical annulus. 



II. Cyath^e^. Sporanges numerous, 

 united in sori on a salient axis, and divided 

 into two equal parts by a vertical annulus. 



III. Gleichenie^. Sporanges united in 

 fours into sori, and surrounded by an oblique 

 annulus, like a turban. 



IV. PARKERiEiE. Sporaugcs not united 

 in sori, and divided into two equal parts by 

 a more or less extensive vertical annulus. 



V. OsMUNDE^. Sporanges united in 

 sori, and covered on the back by a broad and 

 imperfect annulus. 



VI. ScHiz>EE^. Sporanges united in 

 sori, and crowned by an annulus that looks 

 like a skull-cap with radiating streaks. 



POLYPODIEiE.— A subtribe of Polypo- 

 dioid Ferns containing the following genera: 



* Veins pinnate. 

 A. Margins of the fertile fronds not revolute. 



I. PoLYPODiuM, L. Sori globose, seated 

 on the apex or the back of veins or venules. 



II. Marginaria. Sori globose, im- 

 mersed deeply in the backs of veins or 

 venules. 



III. Pleopeltis. Sori globose, seated 

 on the backs of veins and venules, with peltate 

 paraphyses concealing the sporanges. 



B. Margins of the fertile fronds revolute. 



IV. Struthiopteris. Sori globose, 

 seated on the backs of veins and venules. 



** Veins anastomosing, without free veins in 

 the areola. 



V. Dictyopteris. Sori globose, seated 



