DEVELOPMENT OF SPONGES FROM DISSOCIATED TISSUE CELLS. 27 



body of very definite character is produced, the shape, size, and covering layer of which 

 are all fixed as species characteristics. It seems permissible to regard the first case as 

 the habit, still probably universal among sponges, out of which in certain groups a 

 definite gemmule-forming habit sprang phylogenetically. 



Various important and stimulating obsen'ations on certain steps in the process of 

 regressive differentiation that takes place in sponges when they are kept in confinement 

 or have been subjected to overfeeding, to the cold of winter, or to foul water, have been 

 recorded by Metschnikoff," who cites also from his predecessors Carter and Haeckel, 

 and others, especially Lieberkuhn,* Masterman,<^ Bidder,"* and \Veltner.< A detailed 

 study of the cellular changes that take place in this process has recently been made by 

 Maas.^ Maas some years ago announced » that when calcareous sponges are exposed 

 to sea water deprived of its calcium, the living tissue breaks up into cords and rounded 

 masses. Whether such masses were able to transform into sponges he was not able 

 to say, although he suspected that such was the case. At the same time (December, 

 1906), at the New York meeting of the American Society of Zoologists I described the 

 phenomena as they occur in Stylotdla and exhibited the degeneration-regeneration 

 masses, some of them completely transformed into sponges. And in the Proceedings 

 (Science, May 17, 1907) I published a note to the effect that such masses can be pro- 

 duced and that they will transform into perfect sponges. Later in the year Maas 

 published a' communication * touching upon this subject in which he announced that 

 the rounded masses of cells produced in the degenerating Sycoyi are able to transform 

 into functional sponges. Apparently the calcium-free water leaves the sponge proto- 

 plasm in a state that makes further development difficult, for it is clear from Maas's 

 recent paper ^ that the Sycon masses are very slow to transform. Maas's statement 

 with regard to the transformation, moreover, leaves it uncertain as to whether this 

 process is completed or not. The masses in question after some weeks increased in 

 size, developed a gastral cavity, and dififerentiated new spicules (op. cit., p. 100). 



Maas in his recent investigation finds, as I described in 1907, that as the reduction 

 progresses a stage is reached in which the sponge flesh consists of trabeculae made up 

 of several kinds of cells all interconnected to form a syncytium. Maas goes on and 

 traces the history of the several kinds of cells and finds that a process of phagocytosis 

 occurs. Certain granular amcebocytes incorporate and digest the choanocytes and 

 other cells, a mass of these constituting the last stage in the process, the nodule of 



a MctschnikofF. E.: SponRioIoRische .Studien. Zcitschrift fiir wissenschaftliche Zoologie. bd. xxxn. 1879. 



!> Licbcrktihn, N.: Beitriige zur Entwickelungsgeschichte der Spongillen. Archiv fiir Anatomie und Physiologic. J. 

 Muller, 1856. 



f Masterman. A. J.: On the nutritive and excretory processes in Porifera. Annals and Magazine of Natural History (6). 

 vol. 13. 1S94. 



d Bidder. G. P.: The collar cells of Heterocoela. Quarterly Journal of Microscopical Science (2). vol. 38. 1895. 



<Wcltner. W.: Spongillidenstudien II. Archiv fiir Naturgeschichte. jahrg. 1893, bd. i. Spongilhdenstudien V, ibid, 

 jahrg. 1907, bd. 1. 



/Maas, Otto: Ueber Involutionserscheintingen bei Schwaminen und ihre Bedeutung fiir die AufTassung des Spongien- 

 korpers. Festschrift zum sechzigsten Geburtslage Richard Hertwigs. bd. in. 1910. 



s Maas. Otto: Ueber die Einwirkung karbonatfr. Salzlrisungen auf erwachsene Kalkschwamme und auf Entwicklungsstadien 

 dersclbcn. Archiv fiir Entwickclungsmechanik der Organismcn. bd. xxil. hfl. j. December. 1906. 



''Maas. Otto: Ueber die Wirkung dcs Hungers und Kalknitziehung bei Kalkschwammen und andercn kalkausschcidenden 

 Organismcn. Sitzungsberichtc der Gesellschaft fiir Morphologic und Physiologie in Miinchen, 1907. 



