248 PROFESSOR E. RAY LANKESTEK. 



excessively thin coating of a green colouring matter, which 

 to judge by its chemical and optical characters is either 

 identical with chlorophyll or very near to it. These cor- 

 puscles therefore exactly correspond, in regard to their con- 

 struction, with the chlorophyll-bodies of plants. In a 

 certain number of them the surface is quite smooth, others 

 acquire a segmented appearance from grooves and fissures. 

 (See PI. XX, fig. 17a.) Related to the latter are small 

 corpuscles in the course of breaking down, which exhibit 

 angular forms, and instead of a bright green have a dirty 

 dark colouring (PI. XX, fig. 21), and gradually pass over 

 into very small dark brown or even black granules, adhering 

 to one another in little heaps (PI. XX, fig. 19). The 

 number of all these bodies varies greatly according to the 

 nutritional condition of the animal. The green bodies are 

 found chiefly in the marginal region of the cell, and only 

 when they are very abundant.in its basal portion; occasionally 

 they appear to be, as it were, stuck on to the cell-surface, but 

 nevertheless always possess a thin envelope of protoplasm. 

 The free end of the cell never contains chlorophyll- 

 corpuscles ; on the other hand, the brown and black granules 

 are accumulated in that region. 



" In H. aurantiaca and grisea} the endoderm-cells of the 

 foot and tentacle cavities are devoid of form-elements com' 

 parable with the chlorophyll-corpuscles of H. viridis. Only 

 orange, brown, and blackish spherical or angular corpuscles 

 occur, which all exhibit a remarkable resistance to chemical 

 reagents. The epithelium of the stomachal cavity contains 

 however — at least in well-nourished specimens — colourless 

 round or oval dense albuminous corpuscles (PI. XX, fig. 16), 

 which, excepting the absence of chlorophyll, closely resemble 

 the coloured corpuscles of H. viridis, and also exhibit the 

 same transitional forms leading to the dark granules." 



I have introduced into this quotation from Kleinenberg 

 references to the figures of the plate accompanying the 

 present memoir. The only important addition which I have 

 to make to Kleinenberg's statement, as to the structure of 

 a normal chlorophyll-corpuscle oi Hydra viridis, is that very 

 usually there is within the shell or crust of the green- 

 coloured substance one or more minute granules, also 

 coloured green and embedded in the colourless pi'otoplasm 

 of the corpuscle.^ 



' Apparently a synonym of our H.fusca. 



" I would, however, analyse the chlorophyll-corpuscle of Hydra into 

 three elements as follows — (1) chlorophyll or green pigment which can be 

 dissolved out by alcohol, (2) chromophorous substance, which carries the 



