DEVELOPMENT OF SPONGES FROM DISSOCIATED TISSUE CELLS. 9 



preparations shown in figure 8, plate ii, and figure 17, plate iii, and by the cover-glass 

 preparation, figure 9, plate 11. The tissue in this shape flattens and spreads quite as it 

 does in the other types. 



These three types, reticula, discrete massive aggregations, and perforated plates, 

 may all be found on the same slide or shell. Moreover, formations that are transitional 

 between the three types are common. The differences are differences of detail. The 

 important fact is that the sponge cells quickly unite to form small, dense, syncytial 

 masses, and that fusion between these goes on until collections of large size (fig. 7, 8, 9, 17) 

 are produced. The larger collections, like the smaller, have the structure of dense syn- 

 cytia, but unlike the smaller (compare fig. 3 and 6) haveasmooth limiting membrane. The 

 larger collections, like the smaller, exhibit ama'boid changes of shape, although these are 

 perhaps slower than in the small masses. 



The collection of dense syncytial tissue, whatever its shape or size, bears some strik- 

 ing points of resemblance to such an organism as a myxomycete, and such collections 

 may conveniently be called plasmodia. The essential features of the plasmodial state 

 are its simple dense syncytial structure and its slow amoeboid power to change shape and 

 position. A plasmodium has only a temporary and chance individuality. It may fuse 

 with others or be subdivided. It is merely a lump or collection of syncytial regenerative 

 tissue. 



METAMORPHOSIS OF PLASMODIA. 



The flattening of the plasmodial masses, reticula, or perforated plates, and their 

 transformation into thin incrustations constitute a part of what may be called the meta- 

 morphosis of the Plasmodium. The histological details of the metamorphosis may be 

 reserved for a later study. Only the conspicuous and easily observed steps in the process 

 will be here enumerated. 



The first obvious step in the metamorphosis is the appearance of coUenchyma 

 (simple connective tissue consisting of branched interconnecting cells) at the periphery 

 of the mass. The collenchyma begins to appear just before or coincidently with the 

 flattening out of the plasmodium. It may be observed in the living mass. With the 

 formation of the collenchyma, a distinct thin epidermal membrane becomes lifted up 

 from the deeper parts of the plasmodium (fig. 31, pi. v). By the time the plasmodium 

 has been transformed into an incrustation (fig. 10, pi. 11), the peripheral collenchyma 

 with the overlying epidermal membrane exists everywhere. 



Somewhat later flagellated chambers begin to appear in great abundance, and canals 

 develop as isolated spaces which come to connect with one another. A stage in the devel- 

 opment of the canals is shown in figure 11, which represents a part of a typical slide prepa- 

 ration kept two days in the live box. The opaque regions indicate where the dense 

 plasmodial tissue lingers more or less unaltered. The canals extend horizontally through 

 the incrustation, and are so arranged as to form radial systems. Each system is com- 

 posed of a few, usually three or four, main canals. At the center where the main canals 

 meet, an osculum is later formed. Such systems are then efferent systems. The finer 



