ANNUL ATA. 



[ 52 ] 



ANNUL AT A. 



Ordinarily there are a number of ducts 

 grouped near the inner part of each con- 

 centric layer of wood, as in the Oak. In 

 the Sumach a layer of cellular tissue occurs 

 at the boundary of each ring. Li the Coni- 

 fers, the markings result from the greater 

 thickness of the secondary deposits on the 

 walls of the cells in the outer part of each 

 layer, no ducts existing in their wood (fig. 



It seems that these rings cannot be taken 

 strictly as annual rings in all trees, especially 

 in those of equable climate, since they 

 appear to depend upon external influences 

 affecting the activity of vegetation ; and 

 thus, even in temperate climates, a great 

 loss of foUage in the summer, followed by 

 recovery, may produce two rings in one year. 

 In moist tropical climates, where the leaves 

 reappear almost continuously, the rings pro- 

 babij' answer to j^eriods of great renewal of 

 foliage. 



ANNULA'TA, Anellida.— The class of 

 red-blooded worms, &c. 



Char. Elongated animals, living in water 

 or moist earth, not par asitically within other 

 animals ; body usually ringed or jointed ; 

 feet not jointed, and frequently replaced by 

 bristles or retractile setigerous tubercles, 

 llespiration eflected either by external 

 branchiie or by internal vesicles, or by the 

 skin itself. Distinct organs of circulation 

 present, contractile vessels replacing a 

 heart. Nervous system consisting of a 

 single or double ventral cord, furnished 

 with ganglia at intervals, and eueircUng 

 the oesophagus above. 



The skin consists of a very delicate struc- 

 tureless and transparent epidermis, beneath 

 which (in Il(S7)toch(iris (I'iscicola), Clepsine, 

 and Kep/ic/is) there is a layer of cells, Avhich, 

 in the adult animals, presents the appearance 

 of a fenestrated membrane (PL 49. fig. 16). 

 The cells (PL 49. iig. 166) leave spaces 

 between them which appear like holes ; 

 but the addition of acetic acid brings to 

 light in each space a distinct nucleus (PL 49. 

 fig. 16 c), and in very young animals the 

 clear spaces are distinct cells, distinguish- 

 able from the surrounding cells by their size 

 and containing numerous clear vesicles as 

 well as a nucleus. The smaller cells contain 

 a nucleus and numerous nuclear granides. 

 Beneath this cellular layer are numerous 

 large fat-cells, pigment-cells, and connective 

 tissue, the latter consisting of a transparent, 

 homogeneous, semisolid mass. A layer of 

 line but firm fibres, crossing each obliquely, 



is said to be sometimes met with beneath 

 the epidermis and forming a corium or true 

 skin. 



In the Turbellaria, the outermost cuta- 

 neous layer consists of ciliated epithelium. 

 The opalescentand often beautiful!}' coloured 

 skin of many of the Annulata does not gene- 

 rally owe its tints to distinct pigment, but 

 to iridescence produced by the fibres. 



The rings of the body are usually furnished 

 with bristles or hairs, sometimes arranged in 

 tufts, at others covering the greater part of 

 the surface of the body. 



The bristles are most exquisite objects 

 for microscopic observation, displaying the 

 greatest variety of form, constituting lances, 

 spears, knives, saws, sickles, hooks, &c., of 

 innumerable elegant shapes, often curiously 

 jointed, and usually fashioned out of an 

 elastic material that rivals the clearest glass 

 (Gosse). Sometimes fuliaceous appendages 

 cover the body Uke. scales. Most of the 

 Annulata are covered with a kind of mucus, 

 secreted by the cutaneous glands ; some 

 live in leathery tubes or sheaths ; in others 

 a case is made by the consolidation of the 

 secretion from some part of the skin with 

 fragments of shells, grains of sand, &c. ; in 

 others, again, the calcareous tubes appear 

 to be whoUy secreted by a portion of the 

 cutaneous surface. 



The muscular sj/stetn is usually well de- 

 veloped. The muscular fibres are in some 

 arranged in three layers, an outer consisting 

 of annular, an inner of longitudinal, and an 

 intermediate of oblique fibres ; in others 

 there is an outer layer of oblique fibres, an 

 inner of longitudinal, with annular fibres at 

 the two ends of the body. The muscular 

 fibres consist of cylinders, the transverse 

 section of which is rounded (PL 49. fig. 17a), 

 flattened or incurvated (PL 49. fig. 17 i). 

 They are covered externally by a delicate 

 sheath or sarcolemma (PL 49. fig. 186). TJie 

 cylinders themselves consist of a clear, homo- 

 geneous, cortical substance (PL 49. fig. 18a), 

 and an internal cavity (c), the latter being 

 filled with a finely granular substance, in 

 which scattered nuclei are imbedded (PL 49. 

 fig. 17 c). At the two ends of the body, 

 the muscular fibres branch dichotomously 

 (PL 49. fig. 19c). The fibres are usually 

 smooth, but sometimes longitudinally or 

 transversely striated ; this appearance arising 

 either from folds in thesarcolemma or proper 

 sheath, or from the granules being arranged 

 in linear series. 



In the Turbellaria, phe muscular system 



