ABSORPTION OF THE HYDRANTH IN HYDROID POLYPS. 303 



that differ from that in Campanularia. The degeneration of the 

 endoderm is much more rapid, the cells breaking down more 

 completely and filling the digestive cavity with fine protoplasmic 

 granules. Since there is no lamella across the bases of the ten- 

 tacles, the endoderm can also pass out from them more readily. 

 The loss of ectoderm is here also accomplished by the passing in 

 of cells through breaks in the lamella, the edges of which are 

 apt to draw together again. The complete disappearance of the 

 lamella does not occur until a very late stage. At the end the 

 whole of the remaining structure is not always drawn through 

 into the stalk, but an ill-defined mass of protoplasm is often left 

 at the end. 



The constant position of the ectodermal gland cells near the 

 beginning of the stalk throughout the degenerative changes show 

 that there is no drawing of cells into the stem until the final 

 stages. 



The histological evidence thus supports my observations on 

 the living animals, that in Campanularia we have to do with no 

 transformation of the protoplasm due to contact, but with a de- 

 generation of the polyp. Similar changes take place in other 

 hydroids, and occur apparently when they are subjected to 

 abnormal or harmful conditions. 



I wish to express my thanks to Professor Morgan for his sug- 

 gestions and kind supervision of my work. 



