811 



CRLLAfitXA. 



CELL& 



MIS 



The grout appear* to enjoy wide geographical range, occurring 

 from the Arctic Circle to the M>uthern point* of America and Africa. 



.\otamia bttruria. a, natural size ; k, a portion nwiniiflcd. 



Scnfaria Mala, a, natural lite ; 6, a portion high!): migninnl. 



Thin gentu (of which seventeen species re described and figured in 

 Uin ' Cat Brit MIIK.') admits nf division into three subgeneric group*. 

 The upccit!" are for the mort part Australian, and with the exception 



of that described by Savigny, wlm-h might have been procured in 

 the Red Sea, appear to be limited to the Southern llrini*].!. 



The if. hyalira, of which a figure is here given from Lamouroux, 

 appears to be referrible to this genus. 



Mnipra hyalira. a, natural ize ; t, c, ccllnlei majmifiol. 



For the best account of the species of this and other families of 

 the Polyzoa the reader is referred to Mr. Busk's complete* and I 

 fully illustrated 'Catalogue of the Marine Polyzoa' in the collection 

 of the British Museum. [PoLTZOA.] 



CELLASTR^EA. [MjLDBXFHTLLIJU.] 



CELLIPORA. [POI.YZOA.] 



CELLS. The ultimate structure of animal and vegetable bodies 

 consists of minute vesicles which are called Cells. In both animal 

 and vegetable structures these organs are not generally visible to 1 1..- 

 naked eye, as they vary from the 1 -500th to the 1-lOOOOth part of 

 an inch in diameter. In all cases they consist of an enveloping 

 membrane or cell-wall, which incloses in a space more or less enlarged 

 certain constituents, called cell-contents. The nature of the substances 

 which enter into the composition of the cell-walls and constitute the 

 cell-conten{s, differs in the animal and vegetable kingdoms, but there 

 are certain properties which all cells possess in common. Sometimes 

 these properties are called vital, to distinguish them from the pro- 

 l*rtics possessed by inorganic or mineral bodies, which are called 

 physical. It will however be seen that, independent of the formative 

 power by which particles of gelatine, cellulose, &c., arrange them- 

 selves in the form of cells, and again these cells arrange themselves 

 into the forms of organs and beings of a specific form, there are few 

 of the functions performed by cells that may not be referred to the 

 action of physical forces. One of the first and most necessary con- 

 ditions of the cell is, that it shall allow of the passage, through the 

 membrane of which its walls are composed, of those substances by 

 means of which it grows, and which it acts upon for the production 

 of the peculiar secretions which characterise either specific beings or 

 parts of their organisation. This function, which is called Absorption, 

 seems referrible to the physical relations which exist between liquids 

 and gases and the membrane of which the cell-wall is composed. 

 [ABSORPTION.] 



The liquid or gaseous contents which are thus introduced into the 

 interior of cells undergo a variety of changes, according to the position, 

 age, or other circumstances of the cell. Sometimes the fluid that U 

 absorbed appears to be transmitted in compound structures from cell to 

 cell without undergoing any great amount of change. In other cases the 

 most decided chemical changes take place in the elements introduced. 

 The cells of some ports of vegetable structures are an instance of the 

 latter, in which carbonic acid and ammonia are absorbed with water, 

 and converted, either during their passage through the cell-wall, or 

 whilst in the interior of the cell, into cellulose, starch, sugar, protein, 

 and other constituents of the cell. In other parts of plants the cells 

 convey solutions of sugar and other substances without producing on 

 them any change. 



The constituents absorbed into the interior of the cell are the 

 materials from which the cell-wall and all its contents are deriv. .1. 

 The process by which the cell appropriates to itself these matters is 

 called Assimilation. This function is supposed to l>e carried on by 

 an independent force or power iv.-i.ling in the cell, or congeries of cells, 

 which form an organ or a body, and has been called the 'assimilat ,-. . 

 force or property,' ' organising force," ' plastic force.' It is necessary 

 however in this process to separate between the changes by which 

 one substance is convert^! into another, and which is probably the 

 result of ordinary chemical force under other circumstances, and the 

 power or force by which these substances are made to assume definite 

 forms in colls and organs. The latter is a special force in the case of 

 <>ncl> cell, plant, or animal, and to which alone, of the changes involved 

 in the function of assimilation, the term vital can be properly 

 applied. 



The result of the appropriation of the new matter absorbed from 

 without in all cells in their enlargement or growth. This takes placa 

 in two ways : either the new matter is taken up into the interior of 

 the substance of the cell-wall, which is always the case where the 

 cell becomes augmented in size, or it is deposited in the form of 

 layers in the interior of the cell. According as the first mode of 

 growth is regular or irregular will be the form of the cell. The vege- 

 table and animal kingdoms present almost all conceivable form* <>( 

 cells, from the spherical and hexagonal cells observed in the low. r 



