rOLTSTOMELl.A. 



POLYZOA. 



P. aeulfotum. with linear rigid bipiniute frond*; the pinnule* 

 oblique^ deourrent. Common in hedge bank*. 



P~ aiauUrt, with the fronds lax, drooping, bipinnate, pinnules 

 irooeaU below, distinctly stalked. Found in the weal of England, on 

 .bettered bank. 



Manual of Brititk Botany ; Lindley and Moore, The 

 ftnu ofdml Britain and Inland, nature-printed.) 



POLYSTOMELLA. [Foiniiixirwu.] 



POLYTHALAMACBA. [OBTBOCEBATIDJL.] 



POLYTRE'MA. [Mauponiojul 



POLYZOA, frequently termed Bryoaoa, are animal* belonging to 

 the Molluscous Sub-Kingdom, closely allied in some respect* with 

 the TtMiro/a, and especially with the Compound Ascidions, whilst in 

 other* they approach the Brackiopoda. 



The analogies presented in their structure with that in other 

 MulluKou* group* having been pointed out in the article MOLLDSOA, 

 it will be needles* here further to refer to them. The present article, 

 after giving a brief view of the more important structural pecu- 

 liarilie* of the class, will be devoted more especially to their mode of 

 clarification ; but since the term I'olyzoa, here employed, has by no 

 mean* obtained universal adoption, it appears requisite to say a few 

 words explanatory of the reason* which have induced us to prefer 

 that term to the name Bryotoa, more usually employed by many 

 British and by most continental naturalist*. 



Section I. Historical. 



Formerly confounded with the Sertularian and other phytoid 

 ZoojJtyta, or Radiata [POLYPIKKRA], it is only within the last thirty 

 year* that the Polgtoa havV been admitted to their proper place in the 

 animal kingdom, having been advanced in fact from one sub-kingdom to 

 another. Their advance from the Radiata to the Molliuca may be said 

 to date from the researche* of Dr. Grant, contained in his ' Observa- 

 tion* on the Structure and Nature of Fluetnc,' in 1827 ; and of Milne- 

 Edwards, in conjunction with M. Audouin, given in their 'Rc'sume 

 des Recherche* aur lea Animaux sans Vertubres faitcg aux ties 

 Channey,' in 1828. To the former of these observers we are 

 imJBbfrxl for the first intimation of several important facts in the 

 anatomy of these creature* among others, of the existence of cilia 

 on the tentacle*, and the curvature of the intestinal canal, with other 

 particulars of leas importance. He failed however to notice the exist- 

 ence of a *econd or anal orifice to the intestinal canal, a fact of the 

 fcijluat importance, as indicating in that respect their close approxi- 

 mation to the Aicidicc, or tunicate molluscs. This opening was 

 discovered by Milne- Edwards and Audouin, and its importance was 

 by them duty appreciated. In other respects their observations 

 agreed with those of Dr. Grant The existence of this anal orifice 

 was regarded by it* discoverers as sufficient to justify a complete 

 change in the ideas then generally entertained with respect to the 

 natural affinities of these animals with the rest of the Zoophyttt. 

 They .proposed to distribute the animals belonging to the class of 

 Polypi, a* then received, into four principal groups, which are in fact 

 pretty nearly identical with those in which they are at present most 

 generally placed. The fourth of these families contained the Flutlrce 

 and other Polypes whose digestive canal opened on the exterior by 

 two distinct openings, and whose organisation approached that of 

 the Compound Ascidians. 



The Utter das*, though thus distinguished from its apparent allies, 

 received no name from the eminent naturalist* to whom it* foundation 

 was due ; and of the names subsequently applied to it, it remains 

 imply to determine which i entitled to the priority. The appellations 

 propoctd for this claai that have received any acceptation at all are 

 three- /Wyroa, Bryotoa, and Ciliobrachiata. The first of these 

 term* (a* a singular noun) was used by Mr. J. V. Thompson in a 

 Memoir, constituting the fifth part or number of hi* ' Zoological 

 Reaearcne*,' and applied by him "to a distinct cla>* of Polypes 

 hitherto in great measure confounded with the Ifydroida." This 

 paper waa published in December, and probably on the 1st of Decem- 

 ber, 1830. The appellation of Bryotoa was given by Professor 

 Ehrcnberg to tho*e Polype* in which two opening* existed to tho 

 digestive canal, and which he thus distinguished from a second class, 

 termed by him the Anlhuoa, In which but one orifice wa* presented. 

 Hi* paper on the ' Coral* of the Red Sea,' in which this subdivision of 

 the Polyp** wa* first proposed, wa* read, or rather was in part read, 

 before the Berlin Academy, on the 3rd of March 1831. It wa* not 

 eomplcUd however till December 1833, nor published until February 

 1854 ; and thin date, for reasons it 1* needles* here to refer to, should 

 BKMt probably be regarded a* the true date of it* publication. The 

 part of the same writer's ' Symbolic Physictc,' in which the term is 

 tutd, wa* not publiahed till June 1831. Consequently, the earliest 

 date which can by any latitude of admission be given to the first 

 publication of the term flryozoa, i* March 1831, or at least three 

 month* after that of Mr. J. V. Thompion'a ' Researche*,' in which 

 that of Polytoa i* proposed. In a very valuable paper published in 

 the ' Philosophical Transactions' for 1837, Dr. A. Farre proposes to 

 employ the term C'l/ioiracAufa for this clan of Polypes, from the 

 circumstance that then- tentacle* are ciliated. But this term, though 

 appropriate and good, ha* since been but rarely employed, and i* 

 obvioutly without any cUim to priority. 



Section II. Structure and Function*. 



The main point* in the anatomy and structural relations of the 

 Polyzoa will be found under the article MOLLUSC A ; but in order 

 to render the account of their classification (which is properly the 

 subject of the present article) more intelligible, it will be necessary 

 briefly to detail the structural, and with them some of the physio- 

 logical conditions presented in the soft and hard part* of the snimal* 



The Polyzoa may be defined a* Compound Molluscous Animals, in 

 which the nervous system consist* of a single ganglion, situated 

 between the mouth and the anus, having a distinct mouth sutrouuded 

 more or less completely by a row of ciliated tentacles ; usually herma- 

 phrodite, and propagated by bud* or ova ; in the mature state mostly 

 fixed, though some posse** the power of locomotion. 



Though differing widely in external appearance, the animal itself 

 is constructed upon a very uniform type throughout all the subdi- 

 visions of the class, and for this reason, the anatomy of one species 

 or order will, with trifling exceptions,' apply to all. The following 

 account of their structure is, in great measure, taken from that given 

 by Professor Allman in bis 'Report on the Freshwater Polyzoa,' 

 published in the ' Proceedings of the British Association* for 1850; 

 and, with the exception of tho word ' polyzoary,' or ' polyzoarium,' 

 which is here used to express the compound growth formed by the 

 associated animals, instead of ' coBmccium,' proposed by that naturalist, 

 the terms used by him have been adopted 



1. Polypide, to signify the soft or retractile portion of the Polyioon 

 2. Ectocyst and Endocyst, to express the two distinct tunics of which 

 the cells of the polyzoary are formed.; the former being applied to 

 the external and the latter to the internal tunic. The pnrt surround- 

 ing the mouth, upon which the tentacles are placed, is termed, 3, the 

 Lophophore ; and 4, the Perigaatric Space, is the space included 

 between the walls of the endocyst and the alimentary canaL 



But besides these terms, which apply more particularly to tho 

 polypide itself, several others are required in the description of the 

 polyzoary. These are 



Cell, the hard portion of the external tunic, into which in most 

 cases the polypide is capable of being retracted by the action of certain 

 muscles. The parts of the cell are 1, the Mouth, or that opening, 

 as it may be termed, through which the polypide makes its exit and 

 its entrance. The borders of this opening are sometimes furnished 

 with Oral Spines, and it is sometimes closed when the creature ha* 

 retreated into the cell, by a Creaceutic Lip, usually having a cartilagi- 

 nous border, and closed by special muscles. (Pig*. 5 and 60.) In 

 many cases the wall of the cell is of equal thickness and similar struc- 

 ture throughout, but in the Cheilostomatous sub-order the front of the 

 cell, or that side upon which the mouth opens and the animal comes 

 out, very often differs in structure from the rest. That is to say, a greater 

 or lees extent of the front may remain wholly or in great measure mem- 

 branaceoua, as in the genus Mcmbrampora, (Jig. 14); or be filled in by 

 a sculptured or perforated calcareous expansion, as in Catenicetta 

 (./t</. 1, 2),Lcpralia (Jig. 15), and many others. The space thus defined 

 when left membranaceous (as it appears in most if not all cases to be at 

 an early period in the formation of the cell), is termed the Aperture. 

 The border* of the aperture are sometimes furnished with Marginal 

 Spines. In some instances, as in Ca6<reand Scrupoctllaria (sp.), the 

 aperture is protected in front by a curious outgrowth from near the 

 margin, which is termed a Pedunculate Operculum. The back of the 

 cell is that part, of course, which is opposite to the front ; the mouth 

 i* situated at or near the upper part of the cell, and is either terminal 

 or Mil, terminal. Other parts, which may be regarded as appendage* 

 to the cells, but which are not universally present, are certain organs, 

 either of offence, defence, or prehension, termed Avicularia and 

 Vibracula; the former constituting a sort of pincers, and the other 

 consisting of a long, slender, movcablo seta. However diverse in 

 appearance, these two kinds of organs are all constructed upon the 

 raine general type ; that is to say, the organ consul* of a hollow cup, 

 or cell, containing two sets of muscles, for the movements of the 

 mobile limb, the mandible, as it is termed, in the one case, and the 

 reta in the other. The avicularia again arc cither pedunculate and 

 moveable upon the peduncle, or sessile, which latter may be either 

 simply sessile or deeply immersed. The Ovicell is an organ of on arched 

 or globose or pyrifortu shape, found on many of the Cketlottomata aqd 

 on some of the Cyclottomata, apparently destined for the development 

 of ova. In the former class it in invariably situated above the mouth ; 

 and in the latter the analogous organ seems to represent a metamor- 

 phosed cell, and in situation corresponds with the other cells of the 

 polyzoary. 



The importance of the avicularian and vibracular organs, in a syn- 

 tematic point of view, may be estimated from the circumstance that, 

 out of 36 genera of ChciloHtpmatous Polyzoa, 20 include species armed 

 with one or the other, or with both ; and that of 191 species no less 

 than 126 are so furnished. They appear to be confined solely to tho 

 Cheilottomata. 



In many coses the polyzoary is affixed by numerous slender corneous 

 tube*, which seem to be merely subservient to that purpose; these are 

 termed Radical Tubes. 



The Polyzoary, or colony itself, is formed of an aggregation of cells, 

 which throughout the two former orders of the class as here arranged 



