ORIGIN OF THE METAZOA. 113 



away and become amoeboid), it is clear that the sponge in this 

 condition and in the case of Schulze's larva already referred to, 

 is a syncytium, and but little more than a multinucleated 

 Protozoon. It differs from such a Protozoon simply in the 

 greater development of the vacuoles (spaces between the 

 cells) of the central portions, and in the presence of a distinct 

 cortical layer of nuclei. 



In some instances this assumption by a sponge of the Proto- 

 zoon form is much more marked than in the above cases. I refer 

 to the case of the well-known form Haliphysema, described 

 by Hajckel (No. 26) as a sponge with an axial ciliated 

 chamber traversing it, and by Lankester (No. 34) as a mul- 

 tinucleated Hhizopod. It is difficult to believe that either 

 of these distinguished naturalists can have made the mistake 

 implied by their contradictory observations ; and the only way 

 of reconciling the latter that I know of, is to be found in the 

 above view, viz. that Haliphysema, like Spongilla and 

 Halisarca possesses under certain conditions, the power of 

 becoming solid : that in certain conditions in which it was found 

 by Hgeckel, it approximates to the sponge, while under other 

 conditions in which it has been found by Lankester and 

 Saville-Kent it loses its sponge-like structure and comes to 

 resemble a multinucleated Protozoon. There are certain 

 points in Lankester's description of the soft parts which favour 

 this view, e. g. the obviously reticulated nature of the proto- 

 plasm (see particularly fig. 9 in Lankester's paper), the large 

 number of nuclei, and, finally, the germ cells. 



These facts, though not in any sense proofs of the view of 

 the origin of the Metazoa for which I am contending, are at 

 any rate suggestive of it, and, so far as they go, in favour of 

 it. That is to say, they suggest the view that there would be 

 two courses open to a Protozoon after it had reached a size too 

 great for the proper nutrition of its centi-al portion, i. e. a size 

 in which the ratio of surface to mass was unfavorable ; it would 

 either divide, in which case it would remain a Protozoon, or 

 it would develop from its vacuoles a system of connected and 

 specialised channels with a definite communication to the 



