kEClBNT Memoirs oii freshwater rhizopoda, 77 



their separation as an independent group becomes necessary, 

 and that is the monaxial character of the body, enclosed in a 

 single-chambered usually firm and unyielding test ; at one or 

 both ends of the test it possesses a definite and permanent 

 opening for the emission of the pseudopodia. The axis 

 leading therefrom to the opposite side the authors designate 

 the principal or longitudinal axis, although it may in some 

 forms be shorter than that transverse thereto. If the two 

 axes are alike the test, viewed from either end of its " longi- 

 tudinal" axis, will be circular, a simple monaxial fundamental 

 form ; if they are unlike the monaxial fundamental form 

 becomes hilaterally sijmmetrical. In this monaxial funda- 

 mental form, then, of which the bilateral symmetry is but a 

 secondary diff'erentiation, consists the pervading distinction 

 of the Monothalamia from the homaxial Heliozoa. The test 

 is either a pure secretion product of the organism where it is 

 either smooth or of variously ornamented peculiar structure, 

 or it is built up or partly composed of foreign constituents 

 such as arenaceous particles, diatomaceous frustules, &c., 

 cemented together. The pseudopodia proceed outward from 

 the animal within only through the one great frontal opening 

 through which, of course, is carried inwards from without 

 the food, or such an opening occurs (in a very few forms) at 

 both ends (Amphistomata) ; if (as mostly) there be but 

 one opening that extremity may be regarded as the frontal 

 or " oral," the opposite closed end as the " aboral" (Diplo- 

 pola, Hackel), whilst when there are two openings they 

 appear to be equivalent and there is no evident differentia- 

 tion of the poles (Haplopola, Hackel). Still so far as I 

 can see the pseudopodia do appear to be usually given off", 

 notably more copiously and to reach a greater length at one 

 end than at the other. 



The body-mass never advances beyond the dignity of a 

 simple cell ; in the Monostomata the posterior part is usually 

 the more homogeneous and contains the nucleus ; the anterior 

 is the more granular, and usually presents some vacuoles, 

 often contractile. In the Amphistomata the nucleus occupies 

 the middle point between the two openings. In the multi- 

 nucleated Arcellse the nuclei lie towards the margin of the 

 discoid body. 



The pseudopodia are of multitudinous character in the 

 diff'erent genera or species. They are cylindrical, blunt, un- 

 branched, non-coalescing, granuleless, very slow in action, 

 on the one hand, or delicate, linear, or inflammatory, pointed 

 acutely, much ramified, constantly coalescing or highly 

 granular and presenting an active " circulation" and vigorous 



