104 



C. M. CHILD. 



enters through the mouth to some extent, though, so far 

 'liserved, the mouth remains closed until disintegration be- 

 gins in that region. As regards the rest of the body and the 

 stalk, entodermal disintegration is distinctly later than ectoder- 

 mal and is usually without any very clearly marked gradient. 



,, - >i 



. / \ r; 



3 



FIGS. 1-3. Diagrammatic optical sections of Pennaria hydranths to show tin- 

 course of disintegration in lethal concentrations. Fig. i. Ectoderm of proximal 

 tentacles disintegrated half way to base; entoderm beginning at tips. Ectoderm 

 of terminal knobs of distal tentacles disintegrated. P"ig. 2. Ectoderm disintegrated 

 to bases of both series of tentacles; entoderm of proximal tentacles two thirds 

 disintegrated, of distal tentacles half disintegrated. Ectoderm of short stalk 

 below hydranth disintegrating. Fig. 3. Tentacles, hypostomc and apical one 

 third of hydranth body completely disintegrated. Ectoderm of hydranth body 

 disintegrated to bases of proximal tentacles. Ectoderm of stalk intact. 



Here as in Hydra (Child and Hyman, '19, p. 193) the entoderm 

 "I the mouth region is apparently much more susceptible than 

 that of other body regions, a difference which is perhaps associated 

 with specially intense glandular activity in this region, ot which 

 iheiv is some histological evidence. 



