52 A. C. WALTON 



its progress. The primary steps are very slow, but in the case 

 in which the process was watched to its completion, the last 

 stages were extremely rapid and were accompanied by rupture, 

 followed by subsequent regeneration of the torn material in each 

 of the daughter animals. These resultant animals resembled 

 normal actinians in size, shape, and the general number and 

 arrangement of the mesenteries. The tentacles were slightly 

 fewer in number than are those of the normal specimens of equal 

 size. 



When found the double animal A was full of embryos of all 

 sizes, from the ciliated planula to young with twelve tentacles, 

 and it set free an occasional one up to a week before the com- 

 pletion of the fission process. On the dissection of the two 

 daughter animals, a few small planulae were dislodged from 

 among the coils of the acontia. The presence of young was an- 

 other proof of the normal condition of the animals during fission, 

 which probably also was of natural origin.. This similarity be- 

 tween the resultants of such fission and normal animals is paral- 

 leled by the cases of ' circumstantial' daughter pairs of Metridium 

 found by Parker ('99), which could not be distinguished from 

 thousands of other normal individuals except by their peculiar 

 isolated positions. 



Though neither the source nor the cause of these double forms 

 of Actinia has been ascertained, it seerns to "me certain that they 

 could not have resulted from double embryos, and even if the 

 condition began with an injury, the later events show that they 

 ended in a slow but actual process of longitudinal fission, and that 

 they were not permanent forms incapable of further develop- 

 ment. It also seems probable that the animals resulting from 

 such a fission are in all respects similar to specimens arising 

 through the process of normal development from the egg. 



Harvard University, October 1, 1917. 



