254 Dr. G. C. J. Vosmaer on the 



names the "Phyllum," separately descended from the Protozoa, 

 Parazoa^ the remainder Metazoa. Marsliall now stepped for- 

 ward in opposition, endeavouring further to support the opinion 

 which he had previously expressed. lie first said * : — 

 " Porifera and Telifera {sit venid verbo) are two divergent 

 branches of the Coelenterate stock, which have arisen from 

 the common stem-form of the Protactinia." And he now f 

 adds to this : — ^' It may readily be granted tliat tlie ancestors 

 of the Sponges had not yet for very long, perhaps never at 

 all, possessed tentacles, which, however, are something secon- 

 dary ; but they were at least two-layered, and, besides, as we 

 may conclude from the occasionally forthcoming cases of 

 reversion, radiate ; they had a mouth-opening and a gastral 

 cavity, from which gastral canals came off centrifugal ly, and, 

 breaking through the ectoderm, opened freely outwards ; and 

 such creatures are, according to my understanding, under all 

 circumstances true Coelenterates." Schulze \ criticizes the 

 views of Butsclili, Marshall, and the older authors, and himself 

 comes to the conclusion tliat very probably the oldest sponges 

 possessed no radial evaginations of their central cavity, but 

 were, like the Ohjnthus amongst the Calcarea, simply sac- 

 shaped. 



Let us now examine these two views, which so strongly 

 contradict one another. I will begin with Marshall's theory, 

 as it is the most definitely formulated. It rests mainly, as 

 the author himself allows, on the radiate structure, which, 

 however, according to him, the Sponges have lost. He views 

 Sponges as degenerate animals, and indeed degenerate Coelen- 

 terates, a view which Dohrn, ten years before, and also 

 Balfour § had already put forward as possible. Balfour is, 

 however, very doubtful : — " It might perhaps be possible to 

 regard Sponges as degraded descendants of some Actinozoon 

 type, such as Alcyonium, with branched prolongations of the 

 gastric cavity ; but there does not appear to me to be suffi- 

 cient evidence for doing so at present. I should rather prefer 

 to regard them as an independent stock of the Metazoa." I 

 believe every one who has engaged in spongological re- 

 searches is often struck with the idea of degeneration, but 

 cannot always bring this into harmony with other tilings. And 

 hence, perhaps, Baliour's doubt. It appears to me that people 

 have always regarded the question too generally, and, on the 

 other hand, too one-sidedly, and have not thought of the 



* Zeitschr, fiir wiss. Zool. Bd. xxxvii. p, 246. 



t Jen. Zeitsclir. Bd. xviii. 



X Sitzber. Akad. Berlin, 1885. 



§ ' Comparative Embryology,' i. p. 122. 



