CHLOROPHYLL-CORPUSCLES AND AMYLOID DEPOSITS. 251 



Hydra are to be regarded as species distinct from Hydra 

 viridis or as varieties. I incline to take the latter view, 

 since transitional forms are met with, namely, olive-green 

 and bluish-green specimens, which have incompletely 

 developed chlorophyll. 



There is no such clear evidence of the specific identity of 

 Hydra viridis and Hydra fusca as there is of the identity 

 of colourless and green varieties of Spongilla. In the latter 

 case one and the same piece of sponge may be found green 

 where exposed to sunlight, and pale flesh colour where 

 shaded from the light. 



The experiment has not, I believe, been made of main- 

 taining Hydra viridis in obscurity, though Max Schultze 

 obtained in this way colourless individuals of Vortex viridis. 

 Commonly in this country large numbers of a very pale 

 brown Hydra are found associated without the presence of 

 any green specimens. These colourless Hydrse {H. fusca) 

 are larger than the H. viridis usually is. But I know of 

 no character separating the two beyond colour and size. 

 The larger size of H. fusca, if it be regarded as a variety of 

 H. viridis, may well be correlated with the non-develop- 

 ment of chlorophyll, and a less active growth. For though 

 the individual is large it may possibly be less active in budding 

 in H. fusca than in the smaller H. viridis. Small size and 

 rapid fission may go well together with the nutritional advan- 

 tages represented by the possession of chlorophyll-corpuscles. 

 In the endoderm-cells of such spe.cimens oi H. fusca (as 

 described by Kleinenberg for his H. aurantiaca and H. 

 grisea) there are angular and rounded colourless bodies (PL 

 XX, fig. 16 g), which appear to represent in a colourless 

 state the green corpuscles of H. viridis. At the same time 

 they are not definitely spherical, as are the latter. Just the 

 same kind of difi"erence is observed in relation to these cor- 

 puscles between H. viridis and H. fusca as there is between 

 green and colourless Spongilla in relation to their corpuscles. 

 I have not made the experiment of subjecting Hydra 

 fusca to the action of sulphuric acid, a reagent which, as 

 narrated above, develops a green colour in colourless sam- 

 ples of Spongilla. But I have examined carefully some 

 very interesting specimens of Hydra which were found by 

 my assistant Mr. A. G. Bourne in company with Hydra 

 fusca, but which were of an olive green or dull blue green 

 instead of pale brown. 



These exceptional individuals appear to me to have great 

 interest. I found in their endoderm-cells that a certain 

 amount of green pigment was developed, but instead of the 



