178 THE MICROSCOPE. 



that sponges should be placed in the vegetable kingdom : " The living 

 sponge, when highly magnified, exhibits a cellular tissue, permeated by 

 pores, which unite into cells or tubes, that ramify through the mass in 

 every direction, and terminate in larger openings. In most sponges 

 the tissue is strengthened and supported by spines, or spicula of va^ 

 rious forms ; and which, in some species, are siliceous, and in others 

 calcareous. The minute pores, through which the water is imbibed, 

 have a fine transverse gelatinous network and projecting spicula, by 

 which large animalcules or noxious particles are excluded ; water inces- 

 santly enters into these pores, traverses the cells or tubes, and is finally 

 ejected from the larger vents. But the pores of the sponge have not 

 the power of contracting and expanding, as Ellis supposed ; the water 

 is attracted to these openings by the action of instruments of a very 

 extraordinary nature (cilia), by which currents are produced in the 

 fluid, and propelled in the direction required by the economy of the 

 animal." 



On the disputed point of sponges being animals. Dr. Johnston re- 

 marks : " Although I agree with the advocates of the animality of 

 zoophytes in general, I cannot go the length of Ellis in considering it 

 proved that sponges and corallines belong to the same class. Ellis, 

 we have seen, knew that no polyps were to be found in sponge ; and 

 their existence in the pores of corallines was inferred merely from the 

 structure of these latter, and their chemical composition. They have 

 been examined by subsequent naturalists fully competent to the task ; 

 and under the most favourable circumstances, — in particular by Cavo- 

 lini and Schweigger, — and the result has been a conviction that these 

 productions are truly apolypous. Now this fact, in my opinion, deter- 

 mines the point ; for if they are not the productions of polyps, the 

 zoologist who retains them in his province must contend that they 

 are individually animals ; an opinion to which I cannot assent, seeing 

 that they have no animal structure or individual organs, and exhibit 

 no one function usually supposed to be characteristic of that kingdom. 

 Like vegetables, they are permanently fixed ; like vegetables, they are 

 non-irritable ; their movements, like those of vegetables, are extrinsical 

 and involuntary ; their nutriment is elaborated in no appropriate diges- 

 tive sac ; and, like cryptogamous vegetables, or algse, they usually grow 

 and ramify in forms determined by local circumstances ; and if they 

 present some peculiarities in the mode of the imbibition of their food, 

 and in their secretions, yet even in these they evince a nearer afiinity 

 to plants than to any animal whatever." 



Miiller writes on this question : " If, therefore, it is still a matter 



