232 STUDIES IN GENERAL PHYSIOLOGY 



a polyp is present ; or, what is perhaps more correct, Tubu- 

 laria grows in length periodically at its oral end, every 

 period beginning with the formation of a new polyp, and 

 ending when this organ drops off. It is therefore necessary 

 that all the animals of a series of experiments which are to 

 be compared with each other should be in the same phase of 

 growth. Since this does not necessarily occur naturally, I 

 cut off the polyps of all of the animals when a series of 

 experiments was started. In all these then began a new 

 period of growth, in which a polyp was first formed, and 

 after which the stem grew in length (the growing part of a 

 stem being situated close behind the tip of the polyp). 

 I waited until the polyps had dropped off in all the speci- 

 mens, and then I knew that the period of growth was at an 

 end. I then compared the longitudinal growth in the indi- 

 vidual specimens which had been subject to different condi- 

 tions. Since growth always occurs with the formation of a 

 new polyp, it follows, without further comment, that the 

 concentration limits for the regeneration of the polyps are 

 also the concentration limits for the growth of the Tubularian 

 stem. 



3. I cut pieces having about the same length and thick- 

 ness from the stems of a large number of individuals and 

 distributed them equally into various dishes containing sea- 

 water of different concentrations. Every vessel contained 

 seven to nine animals. After eight days, in which time they 

 had formed new polyps and grown vigorously, the Tubu- 

 larians were removed and the amount of new growth was 

 measured. The following table shows the increase in the 

 linear growth of the individual Tubularians. The figures of 

 the first horizontal line show the amount of salt, in per cent., 

 contained in the different solutions used ; in the vertical line 

 under each of these figures is given the increase in the length 

 of the individual Tubularians. 





