194 FRESH- WATER RHIZOPODS OF NORTH AMERICA. 



covered Protoplasts. The sarcode is formed of a basis of pale, granular, 

 colorless protoplasm, not unfrequently presenting a feeble yellowish hue. 

 Diffused through the protoplasm there are numerous fine oil-like molecules, 

 and often an accumulation of these occupies an intermediate zone. The 

 fundus of the sarcode mass is occupied centrally by a large, clear, homo- 

 geneous nucleus, as seen in figs. 1-6. Rarely, as in fig. 7, I have seen the 

 nucleus occupy a lateral position. 



Contiguous to the nucleus frequently the sarcode is mingled with 

 variable proportions of scattered oil-like globules, as represented in figs. 5, 

 7, 9, but these are often absent or minute and inconspicuous, as seen in 

 figs. 1-4, 8. 



The lower region of the sarcode, intermediate to the nucleus and the 

 mouth, is commonly occupied with more or less food materials, consisting 

 of green one-celled alga?, diatoms, etc. The green algae turn red, as a 

 result of digestion. With the food there are often mingled colorless 

 globules of various sizes. Some of these appear to consist of water ; and 

 occasionally I have seen one or more enlarge and collapse. In one instance 

 I observed such a globule approach the mouth (fig. 3) and have its liquid 

 contents expelled. Independently of these water globules, not always 

 present, I detected no distinct contractile vesicle. 



The pseudopods of Pamphagus mutabilis appear as filamentous exten- 

 sions of the protoplasmic basis of the sarcode, finely and obscurely granu- 

 lar in constitution, and without oil molecules. I could never detect any 

 appearance of circulation of granules in the pseudopods. 



The investing membrane or shell of Pamphagus mutabilis is colorless, 

 transparent, and structureless. It is highly elastic, so that it yields to the 

 extension of rigid food, and returns to its normal condition when the extend- 

 ing force is removed. 



PAMPHAGUS HYALINUS. 



Plate XXXIII, figs. 13-17. 



Arcella ? hyalina. Ehrenberg: Infusionsthierchen, 1838, 134, Taf. ix, Fig. viii. Abh. Ak. Wis. Berlin, 

 1871, 235, 264.— Presenilis : Abb. Senok. Resells. 1856-58, ii, 219, Taf. xii, Fig. 1-24. 



Gromia hyalina. Schlumberger : An. Sc. Nat. 1845, iii, 255. 



Difflugia Enchclys. Schneider : Miller's Archiv, 1854, 204, Taf. ix, Fig. 16-24. 



A. Homceochlamys hyalina. Ehrenberg: Abh. Ak. Wis. Berlin, 1871, 244. 



Lecythium hyalinum. Hertwig and Lesser: Arch. niik. Anat. 1874, x, Suppl. 177, Taf. iii, Fig. 8. — Archer: 

 Quart. Jour. Mic. Sc. 1877, xvii, 197, pi. xiii, figs. 1,2. 



Animal spheroidal, and feebly produced at the lower pole into a short, 



