CECROPS. 



[ ns ] 



CELL. 



CECROPS, Leach. — A genus of Crustacea, 

 of the order Siphouostoma, and family Cali- 

 gina. 



C.Latreillii. Found on the sun-fish (OrMa- 

 goriscus molcc). Female, length 1", male 1-3". 



BiBL. Bau'd, Brit. Etitomosi.; V. d. 

 Hoeven, Hanclb. d. Zoologie, i. 



CEDAR.— The Cedar of Lebanon is the 

 Abies or Pinus Cedrus. The fragrant, so- 

 called ' Cedar,' of which pencils, &c. are 

 made, is the wood of Juniperus Virginiana. 



See CoxiFERiE, and Wood. 



CELL, Animal. — The tissues and organs 

 of animals, like those of plants, are in great 

 part made up of cells, but the full-grown 

 structures of animals are strikingly distin- 

 guished from those of vegetables by the 

 departure from or disguisal of the primitive 

 cellular constitution. 



Under the head of Cell, vegetable, 

 the cell is defined as a vesicle or sac consist- 

 ing of a membrane composed of cellulose, 

 containing within it a nitrogenous structure, 

 the vital part, called the primordial utricle. 

 In animals this internal structure mav exist 

 alone, without a membranous envelope form- 

 ing the true cell or closed sac, as in Amoeba, 

 and analogous organisms ; but ordinarily the 

 animal cell, like the vegetable, is a true shut 

 sac, enclosing liquid or gelatinous contents, 

 the membrane, however, being here almost 

 always composed of a nitrogenous compound, 

 and onl}' in a few cases of cellulose or allied 

 substances such as prevail in the solid parts 

 of plants. 



The membrane of animal cells is ordinarily 

 transparent and colourless, mostly smooth, 

 and so thin as to exhibit only a single 

 bountlary line ; more rarely the membrane 

 is tolerably firm, presenting a measurable 

 thickness ; while it is sometimes very thick 

 and appears to consist of several layers. 

 Occasionally the membrane has a granular 

 appearance, arising from projections de- 

 pendent on granules lying on the inside. 

 No structure can be detected in the cell- 

 membrane itself. 



The membranous cell generally contains a 

 liquid, the consistence of which varies ; in 

 this float molecules, granules, globules or 

 other very minute cells. In addition to these, 

 we frequently find one or more of those 

 bodies which are termed nuclei, often 

 attached to some part of the cell-wall. The 

 nuclei again contain nucleoli. The cell- 

 contents likeAAise include, in particular 

 structures, products of secretion, — matters 

 separated by the cells from the circulating 



fluid, as in the cells of the renal epithelium, 

 &c. ; also cr5^stals. 



The forms presented by animal cells are 

 not so varied, or generally so geometrical, as 

 those occurring in the cells of vegetables. 



In regard to size, the larsjest are the volk- 

 cells of ova, especially of Birds and Reptiles, 

 and of some animals consisting of a single 

 cell, as certain of those curious organisms, 

 the Gregarin<E. 



The nuclei are usually spherical or lenti- 

 cular, transparent, and colourless or yellowish. 

 They are sometimes solid or homogeneous, 

 at others they are vesicles, with a very 

 delicate membrane. They sometimes contain, 

 exclusively of the nucleolus, a transparent, 

 colourless or yellowish liquid, in which water 

 and acetic acid produce a precipitate of 

 granules resembling those existing in the 

 cell-contents ; hence in the ordinary manner 

 of examining them, they seldom present 

 their natural transparency. 

 • The nucleoli are rounded, well-defined, 

 very minute, sometimes immeasurable. 



Chemically, the cell-membrane ordinarily 

 consists of aproteine-compound; it is mostly 

 dissolved, or rendered so transparent as to 

 become invisible, by acetic acid and solution 

 of potash. Cell- membranes composed of 

 cellulose occur in some animals, as in the 

 Tunicata, &c.; it is detected here, as in plants, 

 by the action of iodine and sulphuric acid. 

 The nucleoli consist also of a proteine-com- 

 pound ; they are soluble in potash, but not 

 in acetic acid. The action of potash distin- 

 guishes them from globules of fat. It must 

 be remarked that the appearances interpreted 

 to be nuclei and nucleoli, frequently are not 

 respectively identical in kind ; the nuclei are 

 sometimes homogeneous, at others true 

 cells; sometimes they relate to the formation 

 of the cell, at others they are young second- 

 ary cells, vacuoles, &c. ; the same applies to 

 the nucleoli. These important points have 

 not hitherto received sufficient attention. 



Cells are endowed with peculiar vital 

 forces, by which they are capable of absorp- 

 tion and the elaboration of the absorbed 

 matter, of growth, reproduction, and of secre- 

 tion. The entire organism of the higher 

 and most of the lower animals, consists at a 

 certain period of life, of cells alone. 



Formation of cells. — Cells are formed in 

 two ways ; either from a blastema or forma- 

 tive substance, existing without or contained 

 within other cells. The blastema or cyto- 

 blastema is a liquid or a semifluid substance, 

 consisting of proteine, fatty matter and salts. 



