3IO WILSON. [Vol. IX. 



ture of about the size and of the same character as a pore. 

 Such peripheral foramina (/. for.) are not common in Espe- 

 rella, and seem to have no function. 



Flagellated Chambers. — After the larva attaches, PI. XVII, 

 Figs. 36, 37, 38, it is, as has been said, largely composed of 

 formative cells. Other smaller cells, bipolar or otherwise 

 branched, are scattered amongst them. Moreover, all the mes- 

 entoderm cells are united into a network, PI. XVII, Figs. 39, 

 42. The formative cells, many of them at any rate, are multinu- 

 cleate. In PI. XVII, Fig. 46, a group of formative cells is shown, 

 some of which are multinucleate. These possess, besides the 

 central larger nucleus with its nuclear membrane and chromatin 

 mass, one or more smaller peripheral nuclei, each having its 

 chromatin mass with nucleoplasm and surrounding membrane. 

 The peripheral nuclei at first sight look like mere chromatin 

 spots, but more careful study satisfied me they were surrounded 

 by nucleoplasm and a membrane. There are, however, scat- 

 tered about in the cell protoplasm other bodies which stain 

 like chromatin balls, but which are in all probability yolk gran- 

 ules. Two of these are shown in the lowermost cell of PI. 

 XVII, Fig. 46. 



In Spongilla, Gotte (6) has described multinucleate cells, 

 which break up by a process analogous to budding, and form 

 cell-groups which give rise to the flagellated chambers. The 

 multinucleate cells are derived from mesoderm cells containing 

 a nucleus and large yolk granules, the yolk granules becoming 

 transformed into nuclei! Maas (14) has studied the same 

 cells (" Dotterzellen ") in Spongilla, using a differential stain 

 (Lyons blue and carmine, or malachite green and carmine). 

 He thinks that the cells in question contain only a single 

 nucleus, together with a number of yolk granules of varying 

 size. The nucleus stains red, the yolk granules blue. Maas 

 does not believe that these cells are concerned in the forma- 

 tion of the chambers, but describes the latter arising as 

 diverticula from a main entodermic cavity. Maas has also 

 studied (16) what I have called "formative cells" in Esperia, 

 and does not believe they are multinucleate. The bodies 

 which I regard as small nuclei peripherally placed, he thinks 



