1893.] MICROSCOPICAL JOURNAL. 343 



the figlit for the zooh^jrists; then came the tug of \v:ir. The 

 greatest pull vvas given for the latter party hy Grant in 1825, 

 who, having put a stiall sponge in a watch-glass full of sea-wa- 

 ter and looked at it with a microscope, said: "I beh Id for the 

 first time the splendid spectacle of a living fountain vomiting 

 forth from a circular cavity an impetuous torrent of liquid mat- 

 ter, and hurling along in rapid succession opacjue masses whi(!h 

 ii strewed everywhere around. Tiie beauty and novt'lty of such 

 a scene in the animal kingdom long arrested my attention." 

 From thai time to a few years ago the botanists gradually re- 

 lintiuished the sponges, Hogg being the last v/h > did battle for 

 them in 1868. 



'i'lie sponges are now universally acknowledged as animals, 

 but their position in the animal kiniidom is still a maltiir of 

 controversy, some following Saville Kent (not accepting their 

 true sexual reproduction) claim them as Protozoa and class 

 them amongthe Choanollagellata others regard them asMelazoa, 

 some with Haeckel, as Coelenterata, some with Schulze and 

 Polejaeff as having branched ofi" from the Coelenterata at an early 

 stage, whilst others with. Marshall regard them as degenerate 

 Coelenterates having at on-^time lossessed tentacles, nematocysts 

 and mesenteric pouches. By B dfour and SoUas they are re- 

 garded as an iadepeadent phi/Uim or special division of the 

 Metazoa. 



We will now consider iv single sponge, say an Ascctta. Here 

 we liave a hollow sac-like organism at'.ached by one end to a 

 fixed object, while at the other end is a large aperture, the 

 osculam or vent At the sides are numerous small apertures, 

 the pores which lead to the central cavity, the pmagitter. The 

 thin walls arecomposed of an outer layer of cells, the ectoderm, 

 which is a pavement epithelium ; of the inner layer of cells, the 

 endodenn, composed of cells resembling the Choanoflagellata. 

 each having a circular funnel-like collar and a long whip or 

 flagellum ; each of the cells besides a nucleus, has one or more 

 contracting vacuoles which are supp.)S 'd to secrete water, urea 

 and carbonic aciil. Between these two layers of cells is a third, 

 the Mesoderm, composed of different amo?l)oid cells, some lead- 

 ing as it were an independent life, wandering from one place to 

 another at will. By the constant vibration of the flagella of the 

 endoderm a current of water carrying small Infusoria, Diatoms, 



