Regeneration in Hydromediisac 21 



hypostome with the hyclranth proper, the cells remain larger 

 (cf. fig. 59), a condition likewise found in the normal hydranths. 

 The stage of development of the hydranth at which the opening 

 forms seems to vary. In fig. 59 the opening is shown and the 

 tentacles were less than half their normal length. Fig. 60 shows 

 the hydranth almost completely regenerated, tentacles of almost 

 natural size, and the opening has not yet been made. The mouth 

 opening does not form till the hydranth is otherwise completely 

 regenerated. 



The enteric cavity of the regenerating hydranth is more or 

 less filled with a mass of debris (degenerating cells, etc.), some- 

 what similar in appearance to the same condition in Tnhularia. 

 Doubtless this mass is partly composed of some of the cells 

 blocking the opening between the hypostome and the enteric cav- 

 ity at an earlier stage. The protoplasm of Eudendriuni does not 

 contain nearly as many granules as that of Tuhnlaria, and the 

 longitudinal entodermal ridges of the latter are not present, so 

 that this debris is not made up of masses of granules set free by 

 the breaking down of entodermal ridges, etc. The origin of this 

 debris was not fully determined. Whether this debris is cast 

 out of the hydranth, when the mouth ofenin is formed, as 

 Stevens (1902) has demonstrated for T. ineseinbryantheniuin 

 and T. crocca, Avas not determined during the course of the 

 experimental work. 



rENNARIi> 



The early appearance of regenerating hydranths in Pcnnaria 

 is very similar to that of Eudendriuni, viz., an enlarged knob or 

 bulb-like protuberance of the coenosarc, from which tentacles 

 seem to bud. The material on hand was all killed in the early 

 stages of regeneration, so that the complete progress of develop- 

 ment could not be worked out. Some points, however, in the 

 early development seem to be sufficiently important to warrant 

 mentioning them. One very pronounced feature is the great 

 abundance of nematocysts in the regenerating hydranths. The 

 ectoderm of the end and sides of the enlarged knob are very 

 plentifully supplied with nematocysts, and they are more or less 



295 



