Coalescence and Regeneration in Sponges 249 



were hung in bolting cloth bags in an outside live-box. Some of 

 the pieces in spite of such rough handling metamorphosed into 

 functional sponges. 



Even where the embryonic bodies of sponges have a fixed 

 structure and size, as in the case of the ciliated larva, the potential 

 nature as displayed in later development, is not fixed in the matter 

 of individuahty. Such a body (see p. 10) may form a single 

 individual or may fuse with some of its fellows to form a larger 

 individual differing from the one-larva sponge only in size. It 

 is then in spite of its definiteness of shape and size, essentially 

 like a lump of regenerative tissue in that whether it develops into 

 a whole sponge or a part of a sponge depends not on its own 

 structure but on whether it is given a good opportunity of fusing 

 w4th a similar mass. A parallel case to the coalescence of larvae 

 is afforded by the gemmules of fresh water sponges. Mr. M. E. 

 Henriksen in a manuscript account submitted to me a year ago, 

 describes the fusion of gemmules to form a single sponge. 



In the preceding description I have passed over the question 

 as to the precise nature of the cells which combine to form the 

 masses of regenerative tissue. On this point as on the histological 

 details in general I hope to have more to say later. Nevertheless 

 the phenomena are so simple that observation of the living tissue 

 reveals much, probably indeed all that is of fundamental impor- 

 tance. If a fairly dense drop of the squeezed out tissue be 

 mounted at once and examined with a high power (Zeiss 2 mm., 

 comp. oc. 6), the preparation is seen to consist of fluid (sea-water) 

 with a few" spicules and myriads of separate cells. The cells 

 fall into three classes. 



1 The most conspicuous and abundant are spheroidal, red- 

 dish, densely granular, and about 8/« in diameter. These cells 

 which can be nothing but the unspecialized, amoeboid cells of the 

 mesenchyme (amoebocytes or archaeocytes), put out hyaline pseudo- 

 podia that are sometimes elongated, more often rounded and 

 blunt. 



2 There is also a great abundance of partially transformed 

 collar cells, each consisting of an elongated body with slender 

 flagellum. The cell is without a collar, the latter doubtless hav- 



V 



