DEVELOPMENT OF SPONGES FROM DISSOCIATED TISSUE CELLS. 29 



sure, be contended that ectoderm cells eventually recombined to form ectoderm, and 

 entoderm cells to form entoderm. The obivous facts are that the cells all combine to 

 form a solid aggregate in which ectoderm, entoderm, and a central yolk mass later 

 differentiate after the general fashion of ccclenterate planulas. The probable inter- 

 pretation of these facts seems to be that the coenosarcal cells when thus violently 

 treated pass into an indifferent, generalized state. In this state they recombine to 

 form a mass of undifferentiated tissue comparable to a heap of blastomeras, in which 

 differentiation and growth later occur. 



DESCRIPTION OF PLATES. 

 Plate I. 



Microciona prolifera. 



Fig. I. Branched specimen. Xj. 



Fig. 2. Two specimens incrusting on shells. Lobular outgrowths have developed. Xj. 



Fig. 3. Cover-glass preparation photographed in alcohol by transmitted light. Sponge cells were 

 strewn over cover and preparation preserved 40 minutes later. The cells have combined to form small 

 masses, and many of the latter have united to form networks. X8. 



Fig. 4. Cover-glass preparation photographed in alcohol by transmitted light. Sponge cells were 

 strewn over cover and preparation preserved 10 minutes later. Sponge cells have combined in part 

 to form individual masses, in part continuous reticula. X8. 



Fig. 5. \'ertical section of normal sponge, incrusting type. Photograph from stained balsam mount. 

 X30- 



Fig. 6. One of the small sync)-tial masses of a preparation like figure 3, stained with hematoxylin. 

 Balsam mount. Photographed by transmitted light. X160. 



Pl.vte II. 

 Microciona prolifera. 



Fig. 7. Slide preparation photographed in alcohol by reflected light. Plasmodial masses have par- 

 tially transformed into thin incrustation. X^- 



Fig. 8. Preparation similar to figure 7, but Plasmodium had more the character of a reticulum 

 Xi 



Fig. 9. Cover-glass preparation photographed in alcohol by transmitted light. Plasmodium par- 

 tially transformed into incrustation. Xi§. 



Fig. id. Slide preparation photographed in alcohol by reflected light. Slide covered wich con- 

 tinuous thin incrustation developed from plasmodia. No canals or flagellated chambers as yet. XiJ. 



Fig. II. Slide preparation kept two days in live box, photographed in alcohol by transmitted light. 

 Canals have appeared, but the system is not complete, especially as regards the terminal ramifications. 

 X3i- 



Fig. 12. Slide preparation kept six days in live box, photographed in alcohol by transmitted 

 light. Canals well developed. Dark spots are barnacles. XiJ- 



Pl.^TE III. 

 Microciona prolifera. 

 Fig. 13. Slide preparation photographed in alcohol by reflected light. Canals have appeared 



X2. 



Fig. 14. Slide preparation kept eight days in live box, photographed in alcohol by transmitted 

 light. Canal system well developed. Dark spots are barnacles. X4. 

 85079°— Bull. 30—12 3 



