Fresh-water Sponge. 165 



capable of amoeboid movements, which make up the greatei- part of the 

 non-skeletal elements of the Spongiadae, there are to be found in them 

 several other kinds of cells, and even tissue, which however readily re- 

 assumes the form of the independent cells by the fusion of the sarcode of 

 which it was composed ; and it is not therefore necessary to say more 

 than that the better mode of expression for the facts acknowledged by 

 both parties is the one which speaks of each exhalant osculum as corre- 

 sponding not to an individual Sponge, but to an individual colony. 



With reference to the third question, that of the position which the 

 Spongiadae may be considered to hold relatively to the Protozoa on the 

 one hand, to which sub-kingdom they ai'e ordinarily referred, and to 

 the Coelenterata on the other, it is perhaps more coiTCCt to regard them 

 as exemplifying the highest stage of evolution of the former, rather than 

 as being a transition towards the latter of these two types. The distinct- 

 ness indeed of their 'oscula' from their 'pores' would appear to place 

 them in a position of superiority as regards the Coelenterata, in which 

 there is but a single orifice both for the ingestion of aliment and for 

 the ejection from the system of refuse matter. Kolliker has thrown 

 doubt upon the view that certain of the sclerous elements of the oi'gan- 

 isms of the Anthozoa are due to epidermal excretion, and thus one 

 point of distinction between them and the Spongiadae would be done 

 away Avith ; but the external chitinous polypary of the Hydroid Zoophyte 

 will serve always to differentiate it from the Sponge, in which the skeletal 

 elements are always internal. This, however, is perhaps a point of 

 merely secondary importance, as is also the non-secretion by Coelenterata 

 of the siliceous deposits so common in the Sponges. 



For the anatomy and physiology of the Spongiadae, see Dr. Bower- 

 bank, Monograph of the British Spongiadae, 1864-1866, 

 pp. 1-152. 



For the methods to be employed in the examination of Sponges, 

 ibid, i., 225 ; and for their application in the eases of Halisar- 

 cina Bujardinii and Spongilla lacustris, ibid, ii., 225, and Zool. 

 Soc. Proc., 1863, p, 462. 



For the physiology of the ' oscula' and 'pores,' see Dr. Bowerbank, 

 British Assoc. Report for 1857, p. 125, pi. i., figs. 1-7. 



For a diagrammatic representation of the mutual relations of the 

 various parts of a Sponge, see Professor Huxley, Introduction 

 to the Classification of Animals, 1869, p. 15, fig. 4. 



