AINKISTRODESMUS. 



[ 43 ] 



ANNULATA. 



Char. Body colourless, oblong, more or 

 less depressed, covered with a resisting tegu- 

 ment, from an aperture in which two filaments 

 emanate ; one flagelliform and directed for- 

 wards ; the other thicker, trailing and retract- 

 ing the body of the animal; movement slow. 

 2 species : — 



1. A. acinus. Movement directly forwards, 

 colomless, aquatic ; length 1-1280 to 1-810". 



2. A. sulcata (PI. 23. f. 12). Movement 

 vacillating in a circle ; colourless, aquatic ; 

 length 1-1100". 



Dujardin suggests that the Bodo grandis 

 of Ehreuberg is referable to one of these 

 species, as also to the genus Heteromita, 



BiBL. Dujardin, Tnfusoires, p. 345. 



ANKISTRODESMUS, Corda.— A genus 

 of Desmidiacese. 



Char. Cells elongated, attenuated, entu'e, 

 aggregated into faggot-like bundles. 



The cells only differ from those of Closte- 

 rium in their aggregation. Species : — 



1. A.falcatus, Corda {Rhaphidium fasci- 

 culatum, Kiitz.). Cells numerous, crescent- 

 shaped; aquatic; length 1-549"; breadth 

 1-7353"; common (PL 10. fig. 47). 



2. A. fusiformis, Corda.'] Carhhad: nei- 



3. A. convolufus, Corda. J ther of these 

 species are admitted into Kiitzing's Sj^ec. 

 Jig. 



BiBL. Ralfs, Brit.Desmidiece,^^. 179 and 

 222; Corda, Almanach de Carlsbad, 1835, 

 p. 121 ; 1838, p. 199. 



ANNUAL RINGS.— The concentric lines 

 seen in transverse sections of Dicotyledonous 

 stems (fig. 21). 



Fig. 21. 



Cross section of a Dicotyledonous stem with annual 

 rings. 



These markings depend on the difference 

 of the character or condition of the tissues 

 produced at different seasons. Ordinarily 

 there are a number of ducts grouped near 



the inner part of each concentric layer of 

 wood, as in the Oak. In the Sumach a layer 

 of cellular tissue occurs at the boundary of 

 each ring. In the Conifers 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 



Fig. 22. 



^ 



Magnified cross-section of stem of Pinus exhibiting parts 

 of three annual rings, 1, 2, 3. 



existing in their wood (fig. 22). Many 

 modifications occur in tropical trees. 



It seems that these rings cannot be taken 

 strictly as annual rings in all trees, especially 

 in those of equable climate, since they seem 

 to depend upon external influences affecting 

 the activity of vegetation ; and thus, even in 

 temperate climates, a great loss of foliage in 

 the summer, followed by recovery, may 

 produce tw o rings in one year ; in moist 

 tropical climates, where the leaves reappear 

 almost continuously, the rings probably answer 

 to periods of great renewal of foliage. 



ANNULATA, Anellida or Annelida. — 

 The class of red-blooded worms. 



Char. Elongated animals, li\ang in water 

 or moist earth, not parasitically within other 

 animals; body usually jointed; feet not 

 jointed, and frequently replaced by bristles 

 or retractile setigerous tubercles. Respira- 

 tion effected either by external branchiae or 

 by internal vesicles, or by the skin itself. 

 Distinct organs of circulation present, con- 

 tractile vessels replacing a heart. Nervous 

 system consisting of a single or double 

 ventral cord, fm*nished w ith ganglia at inter- 

 vals, and encu'cling the oesophagus above. 



The skin consists of a very delicate struc- 

 tureless and transparent epidermis, beneath 

 which (in Hcemocharis (Piscicola), Clepsine 

 and IS! ephelis), thereisa layer of cells, which, in 

 the adult animals, presents the appearance of 

 a fenestrated membrane (PI. 40. fig. 16). 

 The cells (PI. 40. fig. 16 b) leave spaces 

 between them which appear like holes ; 

 but the addition of acetic acid brings to light 



