EXPLANATION OF PLATE XX.—Condnued. 



derm-cells of Hudra viridis, iu association witii the cliloroplijU-corpuscles 

 (see fig. 21). Fresh, without reagents. 



Fig. 20— a. to /. A number of examples of chlorophyll-corpuscles of 

 Hydra viridis. All are seen in optical section excepting c and g, in which 

 cases a surface view is also given. The green envelope is seen to be in- 

 complete in the examples, a, e,f, h, i. The average diameter of these 

 corpuscles is from s^o^-^ ^^ e 5*00 <^^ ^'i inch. Fresh, without reagents. 



Fig. 21. — Portion of an endoderm-cell of Hydra viridis, showing normal 

 chlorophyll-corpuscles (c), minute rod-like bodies coloured green {cc), and 

 also peculiar brown corpuscles (dr). Fresh, without reagents. 



Fig. 22. — Spherical corpuscles isolated by teazing the endoderm-cells of 

 an olive-green coloured specimen of Hydra fnsca. All three contain angular 

 granules set in the substance of the spherical corpuscle. In a and i, these 

 were seen to be eotourless, in c they were coloured yreew. 



Fig. 23. — Normal chlorophyll-corpuscles of Hydra oiridis from an endo- 

 derm-cell which had been fixed by dilute osmic acid, and subsequently 

 treated with alcohol, so as to dissolve out the green colouring matter 

 (chlorophyll). The cell was then subjected to a prolonged staining with 

 picrocarmiue. The part of the corpuscles originally coloured green by 

 chlorophyll (chromophorous substance) does not stain, but the enclosed 

 protoplasm acquires a pale pink colour. In fig. 15 the staining was not 

 sufficiently prolonged to afi'ect the chlorophyll-corpuscles. 



Fig. 24. — Irregular block-like mass Cy^oot^ '"^h in diameter), from an 

 olive-green specimen of Hydra fusca, naturally coloured green by chloro- 

 phyll, and exhibiting a small enclosed particle of colourless protoplasmic 

 substance, which has been stained by picrocarmine. 



