356 ELEMENTARY BIOLOGY. [CHAP. 



y. Superadded to the cell-protoplasm. In //. 7'iridis 

 \\\Q. chloroplastids ; small round bodies fairly uniform 

 in size, for the most part aggregated at the cell- 

 base. They stain very feebly, and may or may 

 not contain chlorophyll : note the manner of its 

 deposition. 



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. 



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

 Hydra. They are highly amoeboid. Watch the 

 nature of their movements. 



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

 pieces of this ; obvious as transparent shreds of mem- 

 brane with jjarallel 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- 

 gloea, 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, ^^'ork through all your 

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



