THE POSITION OF SPONGES IN THE 

 ANIMAL KINGDOM. 



THERE is no group of animals whose affinities and 

 systematic position have been, from the earliest 

 times to the present day, so much a matter of dispute 

 and uncertainty as in the case of sponges ; scarcely any 

 theory can be imagined, possible or impossible, which has 

 not been put forward at some time or other. It will be 

 the object of this paper, not indeed to attempt to add an- 

 other theory to those already existing, but to discuss the 

 problem of the true nature of sponges in the light of the 

 most recent researches upon the group, in the hope of being 

 able to arrive at a decision in favour of one or the other of 

 the many opposing views. An inquiry of this kind falls 

 naturally into three parts : first, an exposition of the various 

 opinions that have been put forth ; secondly, a brief 

 critical discussion of the leading features of sponge organi- 

 sation and development which are of importance for the 

 question at issue ; and, finally, any conclusions which may 

 be drawn from the facts in favour of one or the other 

 theory. 



Even as late as the middle of this century, the realm 

 of nature to which sponges belonged, whether animal or 

 vegetable, was still a matter of discussion. We need not, 

 however, trouble ourselves with this controversy, long since 

 laid to rest, but we will concern ourselves only with those 

 theories which assign to sponges some place or other in the 

 animal kingdom ; and it will be convenient, in considering 

 the different views that have been expressed, to classify 

 them in order according to the systematic position which 

 they assign to the group. We have then three main 

 classes of theories, each with several subdivisions, accord- 

 ing as their authors group sponges (i) as Protozoa, (2) as 

 a distinct phylum descended from the Protozoa but distinct 

 from the Metazoa, and (3) as Metazoa. 



