I 5 8 SALINELLA 



(2) there were numerous small circular discs in the water ; lie concludes 

 that multiplication is effected by fission or fragmentation. 



The homologies of the cell layers is uncertain ; whereas some authors 

 regard the columnar cells as endoderm, and look on the organism as a 

 flattened-out gastrula, Buteckli regards it as a " placula." There appears 

 to be no reason to believe that the whole external layer is not ectoderm, 

 but whether the internal tissue is mesoderm or endoderm, there is no 

 evidence to show. Possibly Trichoplax is a degenerate, acoelous Turbel- 

 larian, deprived of rod cells. 



Treptoplax, KorotnefF, is somewhat similar, and has been seen in the 

 Naples Aquarium. 1 



APPENDIX III. 



Pemmatodiscus socialis, Montic., 2 is essentially a gastrula, with cili- 

 ated ectoderm, containing rhabdites. One surface is flat, with a small 

 central mouth leading into a distinct enteron. It occurs in cysts in the 

 tissues of Rhizostoma pulmo, and appears to multiply by fission within 

 the cyst ; nothing is known of any " organs." 



APPENDIX IV. 



What was termed Salinella salve by Frenzel, was stated by him to 

 occur in a 2 per cent solution of salt at Cordova, in the Argentine. He 

 describes it as an oval sac, with a wall formed of a single layer of cells, 

 and containing a cavity communicating with the exterior at each end. 

 The " ventral " cells are ciliated ; the dorsal are not ciliated but carry 

 " setae," and all the cells are ciliated at their internal ends. Reproduction 

 is said to take place by fission, and also by multiple fission after encyst- 

 ment and conjugation. The "larvae" are declared to be unicellular 

 likenesses of the "adult" and closely resemble hypotrichous ciliated 

 Protozoa. 3 



If Salinella has a real existence, it forms, as Apathy 4 has argued, an 

 intermediate form between Protozoa and Metazoa, and the term Mesozoa 

 has been resuscitated in this new sense. But there is not sufficient 

 ground for accepting Frenzel's interpretation of his observations. 



So little is known about the anatomy or life-history of Trichoplax, 

 Pemmatodiscus, and Salinella that it is impossible to make any definite 

 statement as to their affinities. Moreover, with the exception of Pem- 

 matodiscus, they have only been met with in a " domesticated " condition 

 in aquaria, and it has been suggested that they are in reality imperfectly 

 developed animals embryos which cannot attain full development owing 

 to these conditions. 



1 See Monticelli, Mitth. Zool. Sta. Neapel. xii. 1896, p. 432. 

 a Monticelli, loc. cit. 



3 Arch./. Naturges. Iviii. 1892, p. 71 ; and Ann. Mag. Nat. Hist. (6), ix. 1892, 

 p. 79. 



4 Annals Mag. Nat. Hist. (6), ix. 1892, p. 465. 



