Grafting of Tubularia 355 



some of the results which I obtained indicate that the great increase 

 in size of the hydranths and the rapidity of their formation in 

 dilute sea-water is due to something more than the difference in 

 osmotic pressure. 



The concentration of the sea-water in the Bay of Naples is 

 estimated at 3.8 per cent. If this water is diluted to 2.5 per cent, 

 growth is increased. Herbst ('04) found that artificial sea-water 

 of the same strength as that of the Bay of Naples was more favor- 

 able for growth of sea-urchin larvae than normal sea-water. I 

 followed Herbst's formula and made a solution of artificial sea- 

 water. I found that growth in this solution was more rapid and 

 also that the hydranths formed in this solution were larger than 

 usual, and lived longer. When the artificial solution was diluted 

 with distilled water, the result was very different from that obtained 

 from diluted water from the Bay. There was no increase in 

 growth or in rate of regeneration. The results showed that the 

 solution was not as favorable for growth as normal sea-water. 

 I concluded from this that osmosis could not be the only factor 

 in determining the increase in growth. It is not altogether improb- 

 able that organic substances in the Bay of Naples exert a retard- 

 ing effect on growth. When these are excluded by preparing the 

 pure artificial sea-water their retarding influence is abolished, and 

 the growth which we consider so unusual is really no more than 

 the normal rate under optimum conditions. This would explain 

 why diluting artificial sea-water does not produce the same result 

 as diluting that which comes directly from the Bay of Naples. 



Child ('07c) has also made a study of the effect of diluting the 

 sea-water. He concludes that the diluted medium increases the 

 energy of the processes which involve hydranth formation. Since 

 I made my experiments with dilute sea-water Child's work has 

 been published. As my results are practically the same as his 

 I shall omit a description of the experiments. 



SUMMARY 



I When two individuals are grafted together changes at once 

 take place in the region of the graft. These changes may not be 



