1 64 NATURE AND AFFINITIES OF THE SPONGES. 



these ciliated bodies, as produced by the Calcispongiae, exhibited an ex- 

 ternal conformation entirely different from his so-called "gastrulae," 

 Haeckel accounted for the inconsistency by declaring that in these special 

 instances the embryonic form was represented by a distinct biogenetic 

 type, which might be conveniently denominated an "amphiblastula." 



Passing on from the foregoing brief record of the peculiar interpretations 

 maintained by Professor Haeckel, with reference to the structure and 

 affinities of the sponges, attention may now be directed to the facts 

 elicited in this connection by the light of most recent research, including 

 those adduced through the investigations of the present author. As 

 an inevitable consequence of the very authoritative declarations of Pro- 

 fessor Haeckel in favour of the Ccelenterate affinities of the sponges, and 

 seeming coincidence of the evidence brought forward with these emphatic 

 statements, the bias of late years has been altogether in the direction of 

 substantiating their Metazoic nature, and of reconciling, with this end in 

 view, the very conflicting structural and developmental data exhibited 

 by the different members of this highly important group. Most note- 

 worthy in this direction is that line of interpretation followed by Metschni- 

 koff, Barrois, and F. E. Schulze, by whom, in both the adult and embryo 

 sponge, the existence of three cellular layers, ectoderm, endoderm, and 

 mesoderm, are distinctly recognized. In conformity with such interpreta- 

 tions, the ectoderm in the adult organism consists of a superficial layer of 

 flattened, simply nucleated cells, closely approximated to each other, and 

 agreeing to a considerable extent with the so-called "syncytium" of 

 Professor Haeckel, this external element being also produced inwards, and 

 lining the cavities of the aquiferous system. The special collared flagellate 

 cells that line the so-called ciliate chambers are accepted as entodermic 

 elements, while to the mesoderm is relegated the remaining interstitial 

 portion, upon which chiefly devolves the secretion of the spicula or other 

 skeletal structures. 



In opposition to the widely supported Metazoic view founded by 

 Professor Haeckel, adhesion is given in this treatise to that interpreta- 

 tion of the structure and affinities of the sponges that first originated 

 with Professor H. James-Clark, and indicated their close relationship to 

 the then small and insignificant little group of Flagellate Protozoa, first 

 introduced to scientific notice by himself, and here described in a greatly 

 extended form under the title of the Choano-Flagellata or Discostomata- 

 Gymnozoida. The immense wealth of material that has been accumulated, 

 both in the direction of the more minute structure of the sponges, and in 

 the extension of our acquaintance with the above special group of Flagellate 

 Protozoa and their allies, since the death of Professor Clark, is found on 

 examination to support the views here adopted to the fullest possible 

 extent. Already, in the 'Annals and Magazine of Natural History' for 

 January and August 1878, and in the 'Popular Science Review' for April 

 of the same year, the leading features of this advocated affinity have been 



