A STUDY OF RESTITUTiaN MASSES. 453 



THE HISTOLOGY OF THE KESTITUTION MASSES. 



Our observations on the histology of the young restitution masses 

 agree closely with those of Wilson, so that it is not necessary for us to 

 describe the younger stages in great detail. 



A section of a young restitution mass from 18 to 24 hours old shows 

 that a perisarc has been secreted, and that it is still in close contact with 

 the cell mass. The central cells are irregular, and show no trace of 

 stratification : the ectoderm and endoderm cells can be recognized, and 

 present a similar appearance to that described as seen in preparations 

 of the freshly squeezed cells, with the exception that the endoderm 

 elements were even less definite, contained no granules and were dis- 

 tinguishable in relatively small numbers : a few of the cells retained 

 their definite outlines, but others were less distinct and appeared to join 

 up with their neighbours by means of pseudopodia-like processes. It 

 would seem probable, as Wilson suggests, that the structure throughout 

 is that of a cellular syncytium, and that even where the cells appear 

 distinct they are united by protoplasmic strands. He also remarks that 

 the endoderm cells form only a small fraction of the syncytium, though 

 they composed a very large part of the mass when fusion began. This 

 he explains by considering that the endoderm cells undergo a transforma- 

 tion which effectually precludes their recognition later, and we would 

 suggest that the majority of these cells take on a plasmodial character, 

 and so by forming a protoplasmic reticulum unite and draw together 

 the other elements of the mass. 



The peripheral cells in contact with the perisarc in these young restitu- 

 tion masses take on an epithelial character quite early, as might be 

 expected from the fact that they have secreted the perisarc. They are 

 distinguishable as a layer of cells resembling those forming the normal 

 ectoderm, with flattened bases in even contact with the perisarc, and 

 they are recognizable several days before any other rearrangement of the 

 cells is apparent in the mass. 



A comparison between sections of early and later stages shows that 

 the nematocysts included in the masses gradually disappear and take 

 no part in the further development. A similar observation has been 

 made by Wilson. 



Sections after 6 days (Fig. 7) show that the cells are much more 

 definite, the individual cell walls show clearly and the nuclei of the ecto- 

 derm cells stain distinctly ; the mass has largely lost its plasmodial indefinite 

 character, much of the cell debris has disappeared and the nematocysts 



