DASYDYTES. 



[ 237 ] DEGENERATION, FATTY. 



The principal filaments are stoutish, 

 branched,andclothedwith branched ramules, 

 upon which are borne the stichidia contain- 

 ing tetraspores (fig. 157), or ceramidia con- 

 taining spores, on distinct plants. Four 

 British species are recorded, of which D. 

 coccinea and D. Arbmcula (PI. 4. fig. 9) are 

 the commonest. 



BIBL. Harvey, Mar. Alga. 93, pi. 12 B ; 

 Phyc. Brit. pi. 40, 224, 225 & 253. 



DASY'DYTES, Gosse. A genus of Ro- 

 tatoria, of the family Ichthydina. 



Char. Eyes absent ; body furnished with 

 bristle-like hairs ; tail simple, truncate. 



I), goniathrix. Hairs long, each hair 

 bent at an abrupt angle j neck constricted j 

 length 1-146" ; fr. wat. 



D. antenniyer. Hair short, downy ; a 

 pencil of long hairs at each angle of the 

 posterior extremity of the body j head with 

 two club-shaped organs resembling antennse ; 

 length 1-170". 



BIBL, Gosse, Ann. N. H. 1851, viii. 198. 



DASYGLCE'A, Thwaites. A genus of 

 Oscillatoriaceae (Confervoid Algee). 



D. amorpha (PL 8. fig. 11) forms a shape- 

 less gelatinous stratum, consisting of curled 

 and entangled filaments, with very large 

 sheaths, open at the ends ; in marshy places. 



BIBL. Eng. Sot. Stipp. 941 ; Kiitzing, Sp. 

 Alff. 272 ; Tab. Phyc. Cent. i. pi. 72. fig. 2. 



DATE. The fruit of the Date-palm, 

 Phoenix dactylifera, N. 0. Palmacese. 

 Roasted dates are used to adulterate real 

 coffee j a so-called date-coffee is also manu- 

 factured from the entire fruit, or from the 

 seed (perisperm) only. The principal tissues 

 of the latter are represented in PI. 2. fig. 9. 



DAVAL'LIA, Sm. A very large genus ; 

 tropical. 



BIBL. Hooker, Syn. 88. 



DAVALL'IE^E. A family of Polypo- 

 diaceous Ferns. 



Fig. 158. 



Fig. 159. 



Davallia pyxidata. 



A pinnule with sori. 

 Magn. 5 diam. 



Davallia. Sori globose or elongate, intra- 



A sorus with the 



indusium cut open. 



Magn. 15 diam. 



or sub-marginal ; indusium terminal on the 

 veins; somewhat urn- or cup-shaped, the 

 mouth truncated (figs. 158 and 159), apex 

 free ; veins pinnate. 



Cystopteris. Sori globose, on the back of 

 the veins ; involucre membranous, sub-or- 

 bicular, inserted by its broad base under the 

 sorus, which at the beginning it covers like 

 a hood ; fronds two or three times divided, 

 thin, veins free. 



DEGENERATION, FATTY. The ab- 

 normal deposition of free fatty matter in the 

 histological elements of animal bodies. 



When, from whatever cause, the normal 

 functions of the morphological element of 

 a tissue cells, or the secondary deposits 

 formed in them become languid or inter- 

 rupted, free globules of fat or oil become 

 deposited in them ; and as this fatty matter 

 increases in amount, the tissue loses to a 

 greater or lesser extent its natural vital and 

 physical properties j hence it is said to be in 

 a state of fatty degeneration. The discovery 

 of the fatty degeneration of tissues is pro- 

 bably one of the most valuable fruits of 

 microscopic study in regard to medical 

 science ; for it has shown us that maladies 

 supposed formerly to arise from too great 

 abundance of the circulating fluid, have really 

 had their origin in a decayed state of.the tubes 

 or vessels in which the fluid was contained, 

 and that the natural process of human decay, 

 as it is called, is a morbid process or disease, 

 probably to a certain extent as remediable 

 or preventible as many other diseases to 

 which man is naturally liable. Here is 

 indeed a matter of deep interest. 



In addition to the deposition of fat within 

 the elements of a tissue undergoing fatty 

 degeneration, amorphous finely granular 

 proteine-matters are sometimes found ; oc- 

 casionally also brown, yellow, red, or black 

 granular pigment is met with (pigmentary 

 degeneration), together with amorphous or 

 crystalline calcareous salts, as the carbonate 

 and phosphate of lime &c. (calcareous de- 

 generation) ; sometimes the fatty matter is 

 crystalline, it then generally consists of 

 cholesterine. 



Fatty degeneration of cells is well seen in 

 those of the liver when undergoing this 

 change. In the normal state, these as well 

 as most cells, except those of true fatty tis- 

 sue, contain merely one or two very minute 

 or no globules of fat, whilst in the dege- 

 nerated tissue they contain a considerable 

 number of larger or smaller globules (fig. 

 160). At the same time, the cell-walls and 



