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XI. 



THE FEESH-WATER SPONGES OF IRELAND. 



By jane STEPHENS, B.A., B.Sc, National Miiseuui, Dublin. 



{Beiiuj the Thirteenth Refort from the Fmma and Floret, Committee.) 



Plates XXVI-XXIX. 



Read Mav 10. PuUislied Septembeh 24, 1920. 



Introduction. 



Sponges constitute the phylum Porifera, the lowest of the Meta^oa or 

 multicellular animals. They are a very isolated group, without any 

 connecting links between them and other groups of multicellular animals. 



The vast majority of sponges are marine, living at all depths, from between 

 tide-marks to the farthest abysses of the oceans. One family only, the 

 Spongillidae, live in fresh water, and certain species belonging even to this 

 family have occasionally been found in brackish ponds and estuaries in 

 different parts of the world. 



Fresh-water sponges exhibit a considerable diversity of structure, and are 

 divided into a large number of genera and species. Of these species, Ireland 

 possesses only five, a contrast to the marine sponges found off our coasts, 

 which are already known to numlier nearly two hundred different kinds. 



Certain marine sponges, namely, the bath- sponge and some of its nearest 

 allies, were known at an early period. There are several allusions to them 

 in the literature ol classical times. Aristotle realized that sponges belonged 

 to the animal kingdom, but after his time opinions on the subject varied. 

 Writing in the year 1824, Gray (" Zoological Journal," vol. i) summed up the 

 views of the earlier naturalists. He writes : — " The true nature of these 

 curious bodies has for a long while been an object of great doubt to all 

 Naturalists, for we find that most of the Aneient Natural //-w^ojv'ww apparently 

 regarded them as animals . . . On the revival of learning ... all those who 

 would examine for themselves considered them as vegetables." Thus we see 

 that during a long period sponges were considered by some writers to he 

 animals, by others plants. As plants they were thought to be most nearly 

 related to the fungi or to the algae. More often they were classed as 

 Zoophyta, or " plant-animals," belonging neither to the animal nor to the 



B.I. A. PKOC, VOL. SXXV, SECT. B. [2 B] 



