A STUDY OF RESTITUTION MASSES. 441 



The especial interest of our investigations lies in the rather anomalous 

 fact that we have not been successful in obtaining regeneration of the 

 complete organism from the dissociated cells. In our experiments the 

 restitution masses, by some rearrangement or metaplastic process taking 

 place among their conglomerated cells, formed tissue aggregates histologi- 

 cally reduplicating the structure of the parent organism, but in a quite 

 irregular and apparently meaningless manner. The masses consisted 

 of irregular convoluted tubules lined with endoderm cells, imbedded in 

 closely packed but irregularly arranged ectoderm cells, among which 

 many isolated endoderm cells were distinguishable, and the whole tissue 

 aggregate was surrounded by a transparent perisarc which it had secreted. 

 Slight contractions and alteration in shape in the cell masses often took 

 place even after several weeks, and many of them remained alive and 

 showed no signs of degeneration for at least fifty days, which was very 

 much longer than the Hydroids themselves could be kept alive under 

 similar conditions. 



Before proceeding further it will be as well to briefly summarize the 

 results obtained by H. V. Wilson. The Hydroids on which he experi- 

 mented were Eudeyidrium carneum Clarke, and Pennaria tiarella Mc- 

 Crady. Proceeding as described in his paper, he squeezed pieces of the 

 Hydroids through bolting silk of 50 and 75 meshes to the inch and then 

 allowed the dissociated cells to form aggregate masses. The following 

 is an abstract of some of his experiments. 



Eudendnu7)i carneum. 



Experiment, July 9. A colony was squeezed, and fusion was observed 

 under the microscope. In a few hours irregular, lobed, flattened 

 masses about 5 mm. wide and 1 mm. thick were formed. By the 

 next day, a perisarc surrounding the whole mass had been secreted. 

 In 4 days outgrowths had formed in which ectoderm and endo- 

 derm could be distinguished. Some of the masses died, but others 

 remained alive. These were isolated, and in 24 hours, one pro- 

 jecting outgrowth ended in a hydranth, and a day later two com- 

 pletely formed hydranths were developed from another mass. 

 These hydranths have the characteristic size, shape, and colour of 

 the normal adult polyp. 



Experiment, July 14. The tissue died before mass formation. 



Experiment, July 15. Flattened plasmodial masses and lumps were 

 formed, but soon died. 



