2(i George Thomas Hargitt 



11. The formation of the distal tentacles of TiibiiJaria larnyx 

 is about the same as in T. crocca and T. tencUa. Proximal ten- 

 tacles form by a combination of evagination and folding, al6ng 

 the whole length, the tentacles being of mature size and form 

 when the hydranth emerges from the perisarc. Xematocysts are 

 found quite commonly in the entoderm and in the debris of the 

 enteric cavity of T. tcncUa and T. larynx. 



12. Regeneration of Eudcndriuui rainosuiii is first indicated by 

 a knob-like protuberance from which the tentacles bud. The ten- 

 tacles start their development as evaginations, involving both 

 ectoderm and entoderm. The entodermal cell at the apex of the 

 evagination divides, and all cells resulting from this division may 

 continue to divide till the entodermal core of the tentacle is 

 formed, the cells being arranged in a single row. Proliferation 

 of cells in the developing hydranth is by mitosis, amitosis also 

 occurring. Increase in the surface of the ectoderm is brought 

 about partly by a change in the form of the cells and partly by 

 cell division. The hypostome develops as an outgrowth of the 

 developing hydranth, cell division also taking place. The proxi- 

 mal end of the hypostome is blocked by a mass of entoderm cells 

 till a comparatively late period. The mouth opening forms when 

 the hydranth is otherwise completely regenerated. 



13. The early appearance of regenerating hydranths of Peii- 

 naria is similar to that of Eiidendrium. Nematocysts are very 

 abundant in the ectoderm of the regenerating hydranths. The 

 layers of ectoderm and entoderm are much thickened and the 

 cells are more abundant, being the result of cell proliferation. 

 Mitosis is quite abundant; and amitosis is also found. 



14. Amitosis is quite abundant in the tissues of the regener- 

 ating hydranths studied. When not followed by cytoplasmic 

 division (as seems to be the case sometimes) it may be for in- 

 creasing the nuclear surface as an aid in metabolism. Amitosis 

 may be the result of special conditions. The explanation of 

 amitosis in regenerating hydroids can not be definitely deter- 

 mined on the present evidence. 



300 



