POIUFEUA [srONGKS]. 



21 



The origin nf these spons^e foimtains had always been a profounrl 1! 

 euij,'ma, whieh Dr. (iraut quaintly compared to that of the then.* 

 mysterious sources of the Nile. In lSi>r» the above-named zoulo^isi i 

 observed small particles beinj^ carried by currents through minute 

 PORES in the general surface of the Jfa/ir/ioiu/ria (Figs. i\ :5n) ; and 

 on account of the presence of these pores, he gave the name I'oiifera 

 to sponges. So much for the entrance and exit of currents : tu 

 ascertain their complete course and their cause, it is necessary U> cut 

 very thin slices of the sponge (Fig. 3). The pores ( Fig. :}nj lead 

 into spaces and channels, which are more or less branched, and which 

 Hnally arrive at the outer surface of groups of spherical cavities 

 termed flagellated or whi]) c;hambers, each jj-j of an inch in 



Fig. 2. 



Ilalichondria panicea (afteT Dr. Grant), n, pores ; e, oscule ; /, ova. Tlio out- 

 ward arrows show the currents escajDing by the oscules ; the inward ones 

 water entering the pores. 



diameter, and with minute orifices in their walls. The whi]> 

 chambers open each by a comparatively large orifice into channels of 

 spaces ; these join with others to form larger and larger canals, 

 which terminate in an oscule. The whip chambers are lined with 

 '•collar-cells" (Fig. ?>('), each of which is provided with a tlagellum 

 or whip and a hyaline collar ; the beating of the whips sets up the 

 currents, which bring in food-particles and oxygenated sea-water, the 

 used-u]) water and debris being driven out through the oscules. 

 Food-particles are taken up bodily by the cells liiiim: the walls of 

 the canals and by the C(.)llar-cells ; but not much is known on this 

 subject at present. The ('.\NAL systk.m from the pon-s t "' 

 whip chambers is termed "in-current," and that fr"'" Mi' ., 

 chambers to the oscules "out-current." 



