Coalescence and Regeneration in Sponges 25 1 



degenerating sponge,^ the evidence from sections, which is the 

 only evidence available in the case, points to the conclusion that 

 the collar cells help to form the syncytial tissue of the masses. 

 The question of interest lying at the heart of this matter may be 

 so formulated: can particles of the Microciona protoplasm dif- 

 ferentiate into functional collar cells and, v^hen the occasion 

 arises, change back into unspecialized masses capable of com- 

 bining with other masses of unspecialized protoplasm to form a 

 regenerative body ? The facts to which I have just alluded sup- 

 port this idea, and indicate that the immediate problem is one 

 worth pursuing farther as a good case of temporary differentiation 

 of protoplasm in the metazoa analogous to the temporary speciali- 

 zation of the cell individual which occurs in such colonial protozoa 

 as Protospongia.' 



As far as the amoebocytes are concerned it is certain that 

 they have great regenerative power. Weltner in a recent paper^ 

 has emphasized the importance of these unspecialized cells in 

 the processes of growth and regeneration. His conclusions which 

 refer directly to fresh water sponges, are that in a growing 

 sponge, in a sponge regenerating new organs after its winter 

 period of simplification, and in the regeneration of a sponge from 

 a cutting, the amcebocytes are the all-powerful elements in that 

 they give rise to all the new tissues formed, He further alludes 

 to the fact that such reproductive bodies as the gemmules of fresh 

 water sponges and the buds of Tethya (according to Maas) are 

 only groups of amoebocytes; further that the gemmules of Tedania 

 and Esperella described by Wilson as developing into ciliated 

 larvae, and the similar bodies found by Ijima in hexactinelhds, are 

 such groups. I may add that the presence of such groups of 

 unspecialized cells in the hexactinellids lias recently been con- 

 firmed by the master in sponge-morphology, F. E. Schulze, who 

 recognizes the probability of their reproductive nature and gives 



3 A new method by which sponges may be artificially reared, Science, n. s., vol. xxv, no. 649, 1907 

 ■• Metschnikoff, Embryologische Studien an Medusen, p. 147, 1886. 



" Spongilliden-studien V. Zur Biologie von Ephydatia fluviatilis und die Bedeutung der Amoebocyten 

 fiir die Spongilliden. Archiv fur Naturgeschichte, 73 Jahrg., i Bd., 2 Heft, 1907. 



