J\IIR\( IIONS OF PROTOPLASMIC MASSES. IO9 



agrees with the amended description of .4. polypora given by 

 Penard ('92; vix: "/rs grande, a bouche tres largement ouverte, 

 et toujoiirs ponrvne de noyaux en nombre considerable.' 1 Appar- 

 ently Hegner i- the only investigator in this country who has re- 

 ported the existence of Arcellae containing many nuclei. Leidy 

 ('79) states that he was able to detect two, occasionally one. and 

 rarely three, though admitting that he had possibly overlooked 

 the presence of some nuclei in the larger forms of Arcella. Occa- 

 sionally large, polynucleated, wide-mouthed specimens were found 

 in my collections. The differences between these two multinu- 

 cleated forms seem to be great enough to justify the creation of 

 a new species. However, if this is done, the law of priority makes 

 it necessary to retain the name .-1. polypora for the smaller torm 

 which was used in these experiments. 



Because of the existing confusion it is deemed advisable to say 

 a few words regarding certain characteristics possessed by the 

 organism studied: shape, structure, and coloration of shell simi- 

 lar to A. discoides; diameter of shell from 80 to 120 micra; height 

 of shell from 25 to 40 micra; oral orifice approximately equiva- 

 lent to one third the diameter of shell; number of nuclei usually 

 eight or ten. Careful scrutiny under the oil immersion failed to 

 reveal any minute pores around the mouth of the shell, but the 

 shadows at the outer margins of the large cancelli lining the 

 buccal aperture might readily be misinterpreted as such under a 

 low magnification. 



Arcella polypora was selected as the object for study because it 

 reproduces rapidly, is easy to culture, and is capable ot with- 

 standing the influences of various stimuli. This rhi/op.xl may 

 be found in either large or small bodies of water, li\ iir^ e-|>t;rially 

 on the under surfaces of aquatic plants, in deca\in^ vegetable 

 matter, and ooze. On April loth. 1922 a < ..IK-i ii<>n, runiaining 

 main" -1. polypora, was obtained from an artificial pool in the 

 botanical garden near the Johns Hopkin- Mi< "logical Laboratory. 

 All of the organisms used in these experiment- \\rre descendants 

 of this lot. A mass culture was kept going, and a- new individuals 

 were needed they were isolated and new (lone- \\viv started from 

 them. 



