356 ELEMENTARY BIOLOGY. [CHAP. 



y. Superadded to the cell-protoplasm. In H. viridis 

 the Chlorelloids ; small round vegetable organisms 

 fairly uniform in size, for the most part aggregated 

 at the cell-base. They stain very feebly, and may 

 or may not contain chlorophyll. 



In H. fusca. The sooty corpuscles ; irregular and 

 transparent, rarely rounded ; sooty particles may or 

 may not be present. Look for the presence of 

 chlorophyll ; occasionally to be found in individual 

 cells. Cf. pp. 344—345. 

 S. Compare the living cells, as obtained by crushing a 

 Hydra. They are highly amoeboid. Watch the 

 nature of their movements. 



e. The mesoglcea. Search under a low power for stray 

 pieces of this ; obvious as transparent shreds of mem- 

 brane with parallel striae. There will be found in 

 connection therewith — 



a. Nuclei and fragments of cells, mostly of the in- 

 terstitial tissue. 



/?. Contractile processes ; firmly adherent to the meso- 

 glcea, the above-named striation being due to their 

 presence. 



Look for fragments in which the two sets of 

 striae cross each other (cf. p. 347). 



y. Compare a piece of the same, obtained from the 

 freshly-killed animal. If forthcoming, press gently 

 upon the cover-glass with the point of a needle; 

 it will be found to be gelatinous and compressible. 



7. Food material and digestion. Work through all your 

 sections under a low power, and look for ingested prey. 



