8 BULLETIN OF THE BUREAU OF FISHERIES. 



sponge cells were strewn over the cover, and the preparation presen-ed 40 minutes later. 

 Independent syncytial masses, some rounded, some irregular, are present. The forma- 

 tion of networks has begun. Between the masses, easily seen at this magnification ( X 1 2) , 

 are abundant very minute masses and free cells. In figure 6 is shown, more highly mag- 

 nified, one of the small syncytial masses of a preparation like figure 3. Other smaller 

 syncytial masses appear in the neighborhood. Figure 4 is a photograph of a cover-glass 

 preparation preserved 10 minutes after the sponge cells were strewn over the cover. The 

 culture drop that was sown on the cover was very thick, and in details this preparation 

 differs from the more common forms. The sponge cells have combined in part to form 

 individual masses but these have very early begun to unite with one another to form 

 extensive reticula. Free cells and minute masses are very abundantly scattered between 

 the masses that are large enough to be distinct at the magnification used. 



As regards the further history of the collections of syncytial masses, such as are 

 shown in figure 3, the details of behavior vary, being largely dependent on the amount of 

 tissue which is deposited in a spot and on the strength of attachment between the mass 

 of tissue and the substratum. Very commonly fusion of the masses, large and small, 

 goes on until coarse reticula are produced. Figure 8 gives a good idea of such a reticulum. 

 The figure is a photograph slightly larger than natural size of a typical slide preparation. 

 The small syncytial masses gradually continued to fuse with one another until a reticuluin 

 was formed composed of cords for the most part 1-2 mm. thick. The sponge tissue was 

 strewn over the whole slide except at the ends, and practically all of the tissue was 

 absorbed into the reticulum. The cords are compact and, except where they adhere to 

 the substratum, rounded. Their structure is that of a dense syncytium, the outermost 

 layer of which forms a smooth limiting membrane. After the formation of such a retic- 

 ulum the peripheral cords begin to flatten out, spreading over the slide as thin incrusta- 

 tions which completely fuse with one another. This is the condition of the preparation 

 shown in figure 8. The flattening out of the rounded compact cords continues, gradu- 

 ally involving the more centrally located parts of the reticulum. Eventually the whole 

 reticulum is transformed into a thin, even incrustation which completely covers the slide. 

 A slide preparation in this condition is shown in figure 10, the incrustation interrupted 

 along the lines where the ties were made around the slide. 



The sponge tissue strewn over the slide (or substratum in general) does not always 

 form a reticulum of cords such as that just described. It often aggregates around sepa- 

 rate centers, forming distinct masses which may be rounded or irregular in shape. Such 

 masses are dense with smooth surface and in structure are quite like the cords. It often 

 happens that on the same slide part of the tissue combines to form a reticulum and part 

 to form discrete masses. This was the case with the preparation shown in figure 7. The 

 separate masses flatten and transform into incrustations as do the cords, and the incrus- 

 tations as they spread commonly unite as described above. 



A third variation may here be mentioned. The small dense syncytial masses of 

 sponge tissue, instead of combining to form an open reticulum, may unite so as to give 

 rise to an expansion interrupted with minute rounded apertures. Such an expansion 

 will be referred to as a perforated plate. This condition is illustrated by parts of the slide 



