rOIUFERA [sr()N(JEs]. 



21 



ases 

 1 and 2 A. n. 



The origin of these sponge fountains had always been a profound High Cases 

 enigma, Avhich Dr. Grant quaintly compared to that of the then Taye'c^^*^ 

 mysterious sources of the Nile. In IS^f) the above-named zoologist 

 obsei'ved small particles being carried by currents through minute 

 POEES in the general surface of the HaUchoadrla (Figs. 2, 3b) ; and 

 on account of the presence of these pores, he gave the name Porifera 

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

 ascertain their complete course and their cause, it is necessary to cut 

 very thin slices of the sponge (Fig. 3). The pores (Fig. 3b) lead 

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

 finally arrive at the outer surface of groups of spherical cavities 

 termed flagellated or whip chambers, each ^^j^ of an inch in 



Fig. 2. 



Hah'rhondria panicea (niter Dr. Grant), a, pores ; e, oscule ; /, ova. The out- 

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

 water entering the pores. 



diameter, and with minute orifices in their walls. The whip 

 chambers open each by a comparatively large orifice into channels or 

 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. 3c), each of which is provided with a flagellum 

 or w'hip and a hyaline collar ; the beating of the whips sets up the 

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

 used-up water and debris being driven out through the oscules. 

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

 the canals and by the collar-cells ; but not much is known on this 

 subject at present. The canal system from the pores to the 

 whip chambers is termed "in-current," and that from the whip 

 chambers to the oscules " out-cui'rerit." 



