3<D2 H. F. THACHER. 



ectoderm and endoderm which are separated by the elastic 

 lamella, which usually meets more or less completely at the 

 oral end after the material of the tentacles and hypostome has 

 been absorbed. At this time the lamella breaks in places and 

 more cells from the ectoderm pass through. There is also a 

 small amount of degeneration on the outside, and by these 

 means the amount of ectoderm rapidly diminishes. Gradually 

 the structure becomes smaller and smaller and finally the last 

 fragment is drawn out of the cup. If there are many cells loose 

 in the body cavity of the polyp at this time, they frequently break 

 through the thin wall and pass out into the water. 



The best guide by which to determine the amount of proto- 

 plasm drawn into the stem, was found to be the masses of nettle- 

 forming cells before alluded to. The cells really drawn represent 

 a very small fraction of the original number. The greater ma- 

 jority have been thrown into the digestive current, from which 

 many are absorbed by the endoderm cells throughout the entire 

 colony. 



To compare the process in Campamtlaria with that in other 

 hydroids, I examined both Eudendrium and Pennaria in which 

 "absorption" also occurs and found the process again one of 

 degeneration. From the time when the first degenerating masses 

 are seen in the digestive current to the final drawing through of 

 the small degenerated mass, the method is almost identical with 

 that in Campanularia. 



Recently there has appeared a paper by Gast and Godlewski, 

 Jr., on the degeneration of the polyps of Pennaria ' who have ob- 

 tained results similar to my own. 2 It is interesting to note that 

 their material was taken from polyps which had regenerated' 

 their heads in the laboratory, and then after two or three days 

 had begun to absorb again a different condition from that under 

 which mine were obtained, yet the process is the same. Since 

 these investigators have fully covered the ground for Pennaria* 

 I shall not describe the changes in that form and indeed merely 

 speak of two or three points in the degeneration of Eudendrium 



1 " Ueber den Regulationsersheinungen bei Pennaria carolinii," Archiv Jiir 

 Entwickehtngsmechanick der Organisnnts, XVI., 1903, 



2 See preliminary note, BIOL. BULL., IV., 2, 1903. 



3 Probably another species. 



