1803.] MrCROSCOPICAL JOURNAL. 343 



the figlit for the zoohigists; then came the tug of war. The 

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

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

 ter and looked at it with a microscope, said: "1 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 opaque masses which 

 it strewed everywhere around. The beauty and novelty of such 

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

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

 linquislied the sponges, Hogg being the last who did battle for 

 them in 1868. 



The sponges are now universally acknowledger] as animals, 

 but their position in the animal kingdom is still a matter of 

 controversy, some following Saville Kent (not accepting their 

 true sexual reproduction) claim them as Protozoa and class 

 them among the Choanoflagellata, others regard them asMetazoa, 

 some with Haeckel, as Coelenterata, some with Schulze and 

 Polejaeff as having branched oft' from the Coelenterata at an early 

 stage, whilst others with Marshall regard them as degenerate 

 Coelenterates having at on^^time possessed tentacles, nematocysts 

 and mesenteric pouches. By Balfour and SoUas they are re- 

 garded as an iadepeiident phylum or special division of the 

 Metazoa. 



We will now consider a single sponge, say an Ascetta. Here 

 we have a hollow sac-like organism atf.ached by one end to a 

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

 oscidam or vent At the sides are numerous small apertures, 

 the pores which lead to the centr.d cavity, the parag inter. The 

 thin walls are composed of an outer layer of cells, the ectoderra, 

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

 endoderm, 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 supposed to secrete water, urea 

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

 the Mesoderm, composed of different amoeboid 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, 



