A STUDY OF RESTITUTION MASSES. 463 



In conclusion, we can say that, experimenting on different species of 

 Hydroids to those employed by Wilson, we have confirmed his results 

 up to the stage of development at which the restitution mass is formed 

 and the perisarc secreted. Beyond that our results differ ; in the species 

 used by Wilson the restitution masses soon gave rise to hydranths, and 

 practically complete new Hydroids were regenerated ; in the species 

 of Antennularia used by us development of the restitution masses was 

 much slower ; they never regenerated hydranths, but gave rise to tumour- 

 like masses of convoluted tubules lined with endodermal cells embedded 

 in masses of irregularly arranged ectoderm cells. These masses remained 

 alive for at least 60 days. 



Our experiments have resulted in the production of masses that are 

 certainly abnormal and pathological, but nevertheless we would submit 

 that the segregation and rearrangement of the cells after isolation, and 

 the comparatively long duration of life of the tumour-like masses to which 

 they give rise are facts of considerable theoretical interest. 



Plymouth, 



March 28th, Vj]2. 



