ORGANIZATION AND GROWTH 



231 



When a transverse incision abc (Fig. 59) is made 

 transversely in a Cerianthus membranaceus fairly near 

 the oral pole, the tentacles T l situated above the incision 

 collapse like the wilted portions of the plant. When I made 

 such a transverse incision in a Cerianthus the tentacles of 

 which were growing actively, the tentacles 

 above the incision ceased to grow, while the 

 remaining tentacles went on. 1 Cerianthus, 

 however, could not be used for a detailed 

 study of the dependence of animal growth 

 upon cell turgor. Longitudinal growth can- 

 not be measured accurately in contractile 

 animals. Moreover, in the experiment on 

 Cerianthus described above the amount of 

 water absorbed by the organs cannot well 

 be controlled experimentally. And, finally, 

 the growth of Cerianthus is relatively slow. 

 I therefore chose a more suitable animal upon 

 which to experiment, namely Tubularia, and 

 a different method of varying the amount of 

 water absorbed the osmotic. I am obliged to Dr. Wort- 

 mann for calling my attention to the plasmolytic experiments 

 of de Yries. 



The stem of Tubularia is surrounded by a rigid periderm, 

 and an increase in length can be measured as accurately in 

 this animal as in the rigid stem of a plant. I changed the 

 concentration of the sea-water through the addition of sodium 

 chloride or fresh water. The temperature was always the 

 same for all the animals in the same series of experiments; 

 the amount of liquid in each vessel was always 300 c.c. ; and 

 the number of animals in each vessel was also nearly always 

 the same. 



2. As is well known, Tubularia grows in length only when 



iSee " Heteromorphosis," Part I, p. 135. 



FIG. 59 



