296 HELEN DEAN KING. 



from 8-20 mm. (Fig. 5). Two days after the operation, there 

 were well developed hydranths on the ends of three branches 

 and only tentacle anlagen on the oral ends of the correspond- 

 ing stems. In two cases hydranths had developed on the end 

 of the branch and also on the cut surface of the stem ; while 

 in the other cases only tentacle analgen were found, and they 

 were equally well-developed on the branch and on the oral 

 end of the stem. During the following two days, hydranths 

 formed on all of the cut ends, sometimes the hydranth developed 

 on the end of the stem before it did on the branch, and some- 

 times the hydranth appeared first on the branch. As a general 

 result of this series of experiments it can be stated that hydranths 

 develop at about the same rate when both the branch and the 

 anterior portion of the stem are approximately the same length. 

 Series 4.-- In the previous set of experiments both the branch 

 and the anterior portion of the stem were of considerable length 

 and both developed at about the same rate. In order to see if 

 similar results would be obtained if the pieces were very short, 

 fifteen experiments were made in which the branch and the stem 

 were cut off about I mm. above their point of union 

 (Fig. 6). When the hydroids were examined three 

 clays after the operation, hydranths were found on the 

 oral end of the stem and not on the cut end of the 

 branch in five cases ; while in four hydroids, polyps 

 had developed on the branch and not on the oral end 

 of the stem ; in the remaining six cases, hydranths 

 were present at the distal end of both branch and 

 stem. 



In those cases in which one or the other cut sur- 

 face failed to develop a hydranth, the ccenosarc appeared to be 

 entirely with drawn from this part. When these stems were ex- 

 amined under the microscope, the streaming of granules in the 

 interior cavity was visible only in the proximal part of the main 

 stem and in the part of the stem or branch that had regenerated. 

 In the cases in which hydranths formed at both cut surfaces, the 

 streaming of granules was found in all parts of the stem and also 

 in the branch. 



In this set of experiments, regeneration seemed to take place 



