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. 



ft. Kleinenbergs fibres (contractile-processes of the 

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

 one, as a parallel series of deeply-stained dots 

 immediately external to a. 



e. Examine the ectoderm under a high power, selecting 

 your thinnest sections. Look for 



a. The larger ectoderm cells (epitheloid layer) ; conical, 

 their bases being external, and fairly uniform in 

 contour. Each is composed of a lightly staining 

 protoplasm, nucleated and at times vacuolated. 

 Note the strong granulation (cuticle) of their free 

 outer borders. 



ft. The interstitial tissue (sub-epitheloid layer) ; composed 

 of aggregates of smaller cells, at the bases of a ; 

 rendered conspicuous by its affinity for the stain 

 and by the great development of nematocysts. 



Cf. sections across a tentacle. The knob-like 

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

 found to consist of aggregates of these cells which 

 have reached the surface. Similar eminences, less 

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

 / Examine, in like manner, the endoderm. 



a. The larger cells (epitheloid layer). Shape, irregular ; 

 size and contour, variable. 



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.' 



