SPONGIDA. 



[ 722 ] 



SPONGOCYCLIA. 



the substance or arranged in bundles form- 

 ing spurious fibres; sometimes projecting 

 more or less from the surface (PI. 45. 'fig. 8). 

 In some sponges they are absent, and in 

 one genus they are replaced by gravel. The 

 calcareous spicula exert a much more 

 powerful action upon polarized light than 

 the siliceous spicula. 



In some sponges, an external membrane 

 is present ; and this has been observed to 

 exhibit a reticular or cellular appearance, 

 from the presence of fine reticular fibres. 



Sponges are mostly marine, rarely fresh- 

 water. In the natural state they often 

 possess lively colours, which appear in some 

 instances to arise from the presence of gra- 

 nules of colouring matter, probably chloro- 

 phyll, in others from iridescence. They 

 usually grow in groups upon rocks, shells, 

 zoophytes, sea-weeds, &c. 



Sponges appear to be propagated in four 

 ways : by gemmation, from the interior of 

 the canals ; by the formation of ciliated gem- 

 mules (swarm-spores) ; by the formation of 

 true sexual ova ; and by the production of 

 bodies analogous to " winter-ova." 



The ciliated gemmules, which are not of 

 general occurrence, are yellowish, oval, 

 narrowed at one end, and covered, except 

 at this part, by vibratile cilia. They are 

 mostly formed in spring, and after swim- 

 ming about for a time, become fixed to some 

 suitable spot and undergo development. 



Of the other reproductive bodies, one 

 kind consists of roundish or ovate masses 

 containing spicula and resembling the 

 parent in structure, either lying loose in its 

 substance, or adherent to the horny fibres, 

 and escaping at its death and solution, to 

 acquire maturity. 



The " winter-ova " are round or ovoid 

 seed-like bodies, with a funnel-shaped de- 

 pression on the surface communicating with 

 the interior. At first these lie in a cavity 

 formed by condensed surrounding substance ; 

 subsequently a membrane presenting a hex- 

 agonal reticular structure is formed around 

 them, upon which a crust of spicula is 

 afterwards deposited. When expelled from 

 the body of the parent, they are motionless j 

 they then swell up, burst, and the minute 

 locomotive germs escape. These exhibit 

 Amoeba-like processes, and take on an inde- 

 pendent life. 



The true ova are oval, and scattered 

 through the general substance ; they have a 

 distinct outer membrane, with a germinal 

 vesicle and spot. The spermatozoa have 



an oval body and a filament ; they occur in 

 minute cells, also diffused through the sub- 

 stance. The germs are ciliated. 



Sponges are probably^ nourished by en- 

 closing Algae &c. in their substance in the 

 same manner as Amoeba. This has been 

 seen to take place in the young animals 

 developed from the winter-ova. 



According to the skeleton, the sponges 

 are divided into three Orders : Myxospon- 

 yice, in which it is absent (Halisarca); Fibro- 

 spongice, in which it is horny or siliceous ; 

 and Caldspongice, in which it is calcareous. 



Thread-cells have been found in the 

 genus Reniera ; and Eimer states that he has 

 even distinguished in some siliceous forms 

 something like connective tissue and fusi- 

 form muscular fibres. 



BIBL. Johnston, Br. Sponges ; Bowerbauk, 

 Br. Spong.) Ray Soc. 1866 ; Huxley, Camp. 

 Anat.; James-Clark, Amer.Jn.ofSci. 1871 ; 

 Gray, Pr. Roy. Soc. 1867 ; Lieberkiihn, 

 Miiller's Archiv, 1856, Ann. N. II. 1868, ii. 

 236; Thomson, Phil. Tr. 1869, and Deep-sea 

 Dredging ; Ellers, Sieb.und Koll Zeit. 1871, 

 xxii. 540; Eimer, Schuttze's Arch. 1872; 

 Leidy, Amer. Nat. 1870; Agassiz, Butt. 

 Harvard Coll 1869; Miklucho-Maklay, 

 Mem. Acad. Petersbourg, 1870; Schmidt, 

 Spongienfauna Atlan. Geb. 1870 ; Spong. 

 Kilste Algier, Spong. d. Adriat. Meer. ; Car- 

 ter, Ann. N. H. 1878, ii. 157 ; ib. 1879, iii. 

 284, 343 ; ib. 1879, iv. 374 ; Gosse, Mar. Zool. 

 i. ; Haeckel, Kalkschwiimme,187'^ ; Vosmaer, 

 Bronn, Klass. $c. t 1882 ; Kent, Inf. 143. 



SPONGIL'LA, Lam. A genus of fresh- 

 water sponges. Two British species, S. 

 fluviatilis and S. lactistris. 



Found attached to stones, old woodwork, 

 &c. in still or slowly running waters ; green 

 or grey. See SPONGIDA. 



SPONGIOLES. Many works on vege- 

 table physiology still retain the old error 

 that the extremities of roots are devoid of 

 epidermis, and that the tissue then presents 

 an open spongy character, whence the name 

 of spongioles applied to the absorbing apices 

 of roots. So far is this from being a correct 

 account of the conditions, that, in reality, 

 not only is the surface completely invested 

 with a continuous epidermis, but the grow- 

 ing point and principal absorbing surface is 

 found a little above the absolute extremity, 

 which is pushed forward by interstitial 

 growth (fig. 679); See ROOTS. 



SPONGOCYC'LIA, Hckl. A g-enus of 

 Radio-flagellate Infusoria. Several species ; 

 marine. (Kent, Inf. 228.) 



