98 Mr. W. Marshall on the 



already been differentiated at all, were lost in all cases, and 

 the radiate structure in most cases, and finally the mesoderm 

 increased in growth to such an extent that, under certain 

 circumstances, the stomachal space and the buccal aperture 

 disappeared. That the ancestors of the Sponges were not 

 for very long, if at all, provided with tentacles, which, indeed, 

 are only secondary, may be readily admitted, but they were at 

 least hilamellar^ and at the same time, as we may conclude 

 from the retrogressions which continually occur ^ radiate ; they 

 had a huccal aperture and a stomachal space, from which 

 gastral canals ran radially to open freely outwards^ breaking 

 through the ectoderm ; and such creatures, to m,y mind, are 

 under any circumstances true Coelenterata. 



When Schulze refers to the developmental processes in 

 Sycon, and comes to the conclusion that it is probable that 

 the oldest sponges possessed no radial diverticula of the gastral 

 space, but, like Olynthus^ had a simple saccular form, we 

 might point out in opposition to this that in many cases onto- 

 geny is no absolutely true reflection of phylogeny, and that, 

 especially the older an animal form (as in this case the sponges 

 undoubtedly are), the more may the phylogenetic recapitula- 

 tion in the individual development be effaced. I might also 

 say that every true Olynthus, like a simple gastrula, is, as an 

 ovate, cylindrical, or conical body, radiate, for through its 

 polar axis we may draw an infinity of longitudinal planes, 

 every one of which will divide it into two exactly similar 

 halves ; this, however, I will not do, seeing that although it 

 is incontrovertibly true, it would sound something like an 

 evasion. But this much is certain — the radial canals and 

 their arrangement are not the exclusive, and perhaps not even 

 the oldest, criterion, of a radiate structure in the Coelen- 

 terata. 



If, however, we look somewhat more closely into the pro- 

 cesses of development, as shown, for example, in the admirable 

 pictorial representations that Schulze* has given us of the 

 ontogenetic processes in Sycon raphanus, it will not be diffi- 

 cult to recognize a true radiate structure in certain stages, I 

 shall lay less stress upon the free-swimming larva with its 

 girdle-ring of granular cells (Taf. xviii. figs. 3-5), although 

 even in it a radiate structure is already expressed ; but let 

 the reader examine especially fig. 12 on Taf. xix., which re- 

 presents a young Olynthus as seen from above. We look 

 down upon the flattened oval extremity of a hollow cylinder, 

 which is perforated excentricallj by a round aperture leading 



* Zeilsclir. f. -n'iss. Zool. Bd. xxxi. Taf. xviii. & xix. 



