and other Indigenous Rhizopods. 449 



if the vacuole for the reception of such particle is formed at the 

 surface (and it unquestionably is so), there is nothing for it but 

 to accord to Actinophrys the power of turning itself inside out 

 after the fashion of Hydra. But even assuming this incredible 

 explanation to be correct, we must remember that in Hydra, 

 after the operation, the external surface becomes differentiated 

 into the normal condition previously existing. In short, here, 

 as in Amoeba, the portion of protoplasm in immediate contact 

 with the surrounding medium becomes ipso facto, and for the 

 time being only, ectosarc; and on no other supposition is it 

 possible rationally to account for the phenomena. 



I have stated that in Actinophrys Eichhornii there is invariably 

 present a line of demarcation between the external and internal — 

 or "cortical" and "medullary" — portions of the structure. 

 This is not produced by any difference in the intimate composi- 

 tion of these two portions, but is entirely dependent on the 

 occurrence of a larger and more symmetrically arranged series of 

 polygonal vacuolated cavities around a smaller and irregular 

 central series. Owing to the uniform size of the former series, 

 and the union of such of their polygonal planes as are nearest 

 the centre of the body, the appearance of a distinct concentric 

 ring is produced. Sometimes, however, more than one ring is 

 observable. This is due to the formation of a second series of 

 symmetrical cavities in the protoplasm. 



My reasons have already been given for discarding the view 

 that the outer and inner portions of A. Eichhornii represent 

 the ectosarc and endosarc as separable from each other. On 

 what then, it may be asked, does the peculiarity referred to 

 depend ? I would answer, on that manifest idiosyncrasy which 

 in one case leads to the formation of a symmetrically sculptured 

 test composed altogether of an exudation from the animal, and 

 in another of a test in which the animal exudation shows no 

 sculpturing, and is merely the basal matter into which mineral 

 or other foreign particles are impacted. And, lastly, I need 

 hardly remind the reader that, in the vegetable kingdom, we 

 constantly meet with manifestations of a like idiosyncrasy, in 

 similar lines of demarcation between the cells constituting the 

 external and internal layers of a leaf or a stem. 



Taking all these circumstances into consideration, I think 

 there is sufficient ground for believing rather that A. Sol, A. 

 oculata, A. viridis, and A. Eichhornii are varietal forms of the 

 same species, at different periods of its history, or engendered 

 by the varying conditions of the medium in which it is found, 

 than that they are specifically distinct forms. 



Allusion has been made to the multiple nuclei of A. Eichhornii. 

 Before briefly describing their appearance, it is desirable that I 



