- 



ZOOLOGY 1-OR MEDICAL STUDENTS 



CHAP. 



,1 t,, (lit other specimens into fine slices or sections for 

 a under the microscope. 



- already indicated is tubular, its cavity (Fig. 32, A, c) 



the coelenteron. The coelenteron communicates with 



: at the mouth : it extends up to the tip of each tentacle 



it ends Mindly. The coelenteron is surrounded by the body wall 



; two layers of cells, an outer ectoderm (Fig. 32, A, ect) and 



771 



ov. 



FIG. 33- 



The structure of Hydra as seen in transverse sections, x 150. A, Normal structure ; B, early 

 Uge of <> ' : ;-. ect, Ectoderm ; E, egg ; end, endoderm ; i.c, interstitial cells of ectoderm ; 



m, moogl'x .1 : m.t, muscular tail of ectoderm cell, lying in close contact with mesogloea and seen 

 i section ; ov, ovary ; /, t. 



an inner endoderm (end), separated by an apparently structureless 



i he mesogloea (Fig. 33, A, m). The ectoderm (Fig. 33, A ; ect) 



real part made up of tall columnar-shaped cells which taper off 



towards their inner ends and there pass into two tail-like prolongations 



in line with one another resemble the crosspiece of a letter T 



'. This crosspiece is in great part composed of protoplasm 



like the inyoneme of a Protozoon, is specialized in the direction 



of extreme contractility. 



