A STUDY OF KESTITUTION MASSES. 443 



It is noteworthy that in Wilson's experiments the restitution masses 

 which did not develop so far as to produce hydranths in every case died 

 within a few days, while in our experiments, though none of the restitu- 

 tion masses produced hydranths, yet many of them remained alive for 

 at least 60 days. Wilson does not state how long the masses which gave 

 rise to hydranths in his experiments remained alive. 



METHODS AND TECHNIQUE. 



The species used by Wilson at Beaufort N.C., U.S.A., were not avail- 

 able at Plymouth. The species on which most of our experiments were 

 carried out were Antennularia ramosa and Antemiularia antennina. 

 Species of Tubularia, Plumularia, and Clava were also tried, but did not 

 give satisfactory results ; though many of these produced restitution 

 masses from their dissociated cell's, yet these masses did not remain alive 

 for more than a few days, and accordingly Antennularia rainosa or A. 

 antennina were used in all our later experiments. 



All material was obtained from Plymouth Sound, inside the Break- 

 water. 



The method of obtaining the isolated cells was the same as that em- 

 ployed by Wilson. Squares of bolting silk of 50, 75, and 180 meshes 

 to the inch were thoroughly washed and finally rinsed out in boiling 

 water. A good sized colony of x4.ntennularia was then cut up into small 

 pieces about a quarter of an inch long and these pieces were laid in a 

 heap in the middle of a square of bolting silk, which was then folded over 

 so as to make a small bag containing the fragments of the Hydroid. This 

 bag was then squeezed with a pair of wooden forceps into a watch- 

 glass containing a little sea-water. With a quite moderate degree of 

 pressure the body cells of the Hydroid are forced out of the cut ends of 

 their protecting tubes of perisarc and then through the meshes of the 

 bolting silk, and by this process become separated into isolated cells 

 or small cell aggregates which collect as an even layer at the bottom of 

 the watch-glass. It is necessary that a sufficient amount of material 

 should be used to form a complete layer of isolated cells at the bottom 

 of the watch-glass about 1 mm. thick, if the formation of restitution 

 masses that will show any degree of subsequent development is required. 



The watch-glasses containing the isolated cells were slightly shaken 

 and rotated so as to bring the cells together as much as possible, and then 

 when they had aggregated to some little degree the watch-glass was im- 

 mersed in a finger-bowl of sea-water. It was found advisable to place 



