M. E. Penard's Notes on some Heliozoa. 149 



covered by a layer of greyish plasma, rather thick at the base 

 and very fine at the apex of the pseudopodiura, and in which 

 regular but very slow movements of granules have been 

 recognized. The axial thread, which may be seen even in 

 the interior of the inner plasma of the animal, where it abuts 

 against the nuclear membrane, presents the curious pheno- 

 menon that under certain circumstances it may completely 

 dissolve and disappear from sight, to reappear an instant 

 afterwards. Hitherto we have not succeeded in explaining 

 this phenomenon ; some authors have imagined an actual 

 retreat, in which the thread would roll up upon itself, but 

 this attempt at an explanation cannot be sustained, for besides 

 that one would easily see the thread in the rolled-up state, I 

 have several times in compressed specimens witnessed the 

 slow dissolution of this thread, the outlines of which, gradu- 

 ally losing their distinctness at the same time throughout the 

 whole length of the thread, finally disappeared completely at 

 the same time that the pseudopodium became Amoeboid. 

 Perhaps we have here only what may be called a voluntary 

 and facultative hardening of the axis of the pseudopodium, re- 

 sembling what takes place at the surface of the body of the 

 Amcebaj and other Protozoa in which the ectosarc is viscous 

 or, on the contrary, resistant and non- glutinous at will. 



The pseudopodia in their entirety present very interesting 

 phenomena ; at one moment rigid and elastic, like steel wires, 

 they will become all at once soft and indifferent, without, 

 however, always changing their form ; exposed to a shock 

 (produced, for example, by a violent stream of water), they 

 will retract themselves suddenly into a single mass, to push 

 out again in a few minutes and attain a length double that of 

 the body. The pseudopodia of Actinosphcertum } shorter rela- 

 tively to the diameter of the animal, are absolutely similar to 

 those of ActinophrySj as indeed is the case with the whole 

 animal, which differs so little from the latter, that I have often 

 been tempted to derive it from a simple colony of Actino- 

 jphrys, but a colony fixed as such in the sequence of genera- 

 tions and resembling the colonial Radiolaria. 



As to the pseudopodia of the Acanthocystides, they are 

 distinguished from those which we have just been considering 

 by a much more considerable fineness and at the same time 

 by a much greater comparative length. They are composed 

 of a rigid thread, upon which are sprinkled small granules of 

 grey plasma, united to each other no doubt by a sort of proto- 

 plasmic varnish. The granules, with the varnish, would then 

 represent the greyish covering of the pseudopodia of Actino- 



