294 PROF. ALLMAN OK THE EKCENT EESEAECHES 



ment of the pseudopodia. GrenacLer has described a central 

 rather large stellate space containing a clear liquid, and having 

 in its centre a little spherical corpuscle, from which radiate a 

 multitude of very fine lines which he believes to represent the 

 continuation of the axis-filaments of the pseudopodia. This obser- 

 vation has been accepted in its essential points by GrreefF, though 

 neither Archer nor Hertwig and Lesser have as yet succeeded in 

 satisfying themselves of its correctness. 



Eeproduction takes place by a direct division of the entire 

 animal into two parts. Greeff has also observed a peculiar en- 

 cysting process in which the sarcode body withdraws itself from 

 the outer walls, contracts into an internal globe, and becomes sur- 

 rounded by a hyaline organic membrane. The spines still re- 

 main on the outer walls ; but the pseudopodia have disappeared, 

 and the surface becomes covered by a delicate hyaline, but strong 

 and impenetrable, siliceous investment. The pale glistening 

 homogeneous spherules which accompany the green granules 

 now undergo a rapid increase, and are probably the spores of the 

 Acanthocystis ', but Greefi" has not succeeded in following the 

 process further, and its true import remains undetermined. 



Notwithstanding the fact that Acantliocystis is destitute of 

 the essential points of Eadiolarian structure enumerated above, 

 Greeff maintains its close affinity to the Eadiolaria. The outer 

 siliceous skeleton, with pseudopodia emitted between the spines, 

 and having their firm axis coming from the interior of the proto- 

 plasm, and apparently from a central capsule-like structure, are all 

 points on which he insists as afibrding evidence of close Eadiolarian 

 relations ; and he accordingly assigns to Acanthocystis a position 

 in the neighbourhood of the Acanthometridse of Haeckel. 



Some other species oi Acanthocystis have also been described. 

 Of these, A. spinifera,(jrieeS, has been well studied by Hertwig and 

 Lesser, who have pointed out a very decided differentiation between 

 ectosarc and endosarc. They describe contractile vesicles in the 

 ectosarc, and in the endosarc an eccentric nucleus with nucleolus. 



Among other forms which are characterized by the presence of 

 certain hard or skeletal structures must probably be placed the 

 genus Astrodisculus of Greeff. 



Greeff gives the generic name of Astrodisculus to certain 

 freshwater Ehizopoda, among which he has distinguished several 

 species, which are all rendered striking by the central sarcode 

 • body being svirrounded by a broad clear zone. This outer 



