PENNARIA TIARELLA McCRADY 



' \ 



FIG. 5. Schematic drawing of a section through the wall of a hydrozoon, 

 after Dalage and Herouard, somewhat modified, ep, ectoderm; msg, meso- 

 glcea; end, endoderm; ggl, ganglionic cell; mcl, muscular fibres; nf, nerve fibre; 

 c, palpocil; cue, cnidocil; pd, peduncle; cpl, external layer of capsule; cpi, 

 internal layer of capsule; cr, hooks; fl, filament; op, operculum. 



different from those in the hydrocaulus. The ectoderm con- 

 sists of an epithelial and a subepithelial layer. The epithelial 

 layer is composed of indifferent and a few myo-epithelial cells, 

 i. e., cells with a contractile process or muscular fibre at their 

 base. All ectodermal muscular fibres belong to the longitudinal 

 system of fibres. In the sub-epithelial layer are found among 



