Factors of Form Regulation in Harenactis Attenuata 473 



a considerable space in the enteric cavity, so that even when the 

 water has been almost entirely forced out of the cavity by extreme 

 contraction, the body still retains its cylindrical shape, because 

 the cavity is filled by the large muscles and other organs. The 

 twenty-four tentacles vary in length from twenty to forty milli- 

 meters according to the degree of distension and various other 

 conditions. Apparently there is no close correlation between the 

 size of the animal and the length of the tentacles, for in small 

 individuals the length of the tentacles is very commonly nearly or 

 quite as great as in large (Cf. Child '05b, pp. 272-274). 



For certain lines of experiment the species has proved to be 

 most favorable material, though the power of invagination of the 

 oral end and the presence in the enteron of the large muscles are 

 complicating factors in many cases. In my experiments the 

 . animals were kept in bowls contammg one to two liters of water 

 according to the number of animals. The experiments extended 

 over four and a half months and many individuals were kept 

 during the whole time. No attempt was made to feed the ani- 

 mals: probably they obtained a certain small amount of food from 

 the water, which was renewed every few days, but a considerable 

 decrease in size was observed during the experiments. Aside 

 from this decrease in size and the change in shape (Child '09), 

 however, a large number, both of whole individuals and of the 

 products ot experiment were apparently in perfectly good condi- 

 tion at the end of the time. 



In the present paper the wound reaction and the course of resti- 

 tution under certain varied conditions, including section at dif- 

 ferent levels are described. The figures are diagrammatic: Figs, i 

 and 2 are about two-fifths natural size, the other figures except 

 Figs. 4 and 5 and ^^3 and 24 about one-fourth to one-third above 

 natural size. 



I THE REACTIONS TO THE WOUND 



In Harenactis, as in other actinians which I have examined, the 

 first reaction to the wound consists in contraction of the regions 

 adjoining the wound. This reaction seems to be characteristic 



