352 ELEMENTARY BIOLOGY. [CHAP. 



which stains deeply. Examine this under a high 

 power and look for 



a. the mesoglcea or supporting lamella; visible as the 

 above-named line. 



/?. Kleineribergs fibres (contractile-processes of the 

 ectoderm-cells) ; obvious, if the section be a good 

 one, as a parallel series of deeply-stained dots im- 

 mediately external to a. 



s. Examine the ectoderm under a high power, selecting 



your thinnest sections. Look for 



a. The larger ectoderm cells ; conical, their bases being 

 external, and fairly uniform in contour. Each is 

 composed of a lightly staining protoplasm, nu- 

 cleated and at times vacuolated. Note the strong 

 granulation of their free outer borders. 



/?. The interstitial tissue ; composed of aggregates of 

 smaller cells, at the bases of #; rendered con- 

 spicuous by its affinity for the stain and by the 

 great development of nematocysts. 



Cf. sections across a tentacle. The knob-like pro- 

 tuberances previously seen (Sect. 2 a. /?) will be found 

 to consist of aggregates of these cells which have 

 reached the surface. Similar eminences, less regu- 

 larly disposed, will be found in the body-wall. 



/ Examine, in like manner, the endoderm. Its larger 

 cells will show 



a. Shape, irregular ; size and contour, variable. 



ft. The cell-protoplasm; largely replaced in one or 

 more clear vacuoles. It forms peripherally a cell 

 membrane, and is generally densest at the base, 

 where it is aggregated to form the so-called 'foot'. 



