GENUS AMCEBA— AMCEBA VERRUCOSA. 57 



The creature does not put forth distinct pseudopods; but in progression 

 the ectosarc rolls forward, appearing at the moment as if it were being 

 drained off from the endosarc, while this as incessantly streams on and 

 maintains the same relative position. 



The contractile vesicle habitually occupies a position at the posterior 

 extremity of the endosarc, but is sometimes propelled forward, even to the 

 middle of the latter. It exhibits its peculiar movements more frequently 

 and expands to a proportionately greater degree than in the adult. In 

 collapsing it usually closes from within outwardly so as to assume at first 

 a reniform and then a crescentoid appearance; but in other instances it 

 closes so as to appear like a decreasing lens. It is very mobile, and, in the 

 irregular contractions of the posterior part of the animal, often assumes 

 an irregular outline of form. It frequently reappears in a group of from 

 two to half a dozen vesicles of different sizes, and these, as they expand, 

 become irregularly confluent until finally they form together a single large 

 sphere. See figs. 9, 15, 16. 



The nucleus appears as a spherical or oval, faintly granular body, 

 often surrounded by a hyaline envelope. Occasionally two such bodies 

 are present. Besides the nucleus and the contractile vesicle, the endosarc 

 frequently exhibits nothing, except some minute oil-like molecules. 



The food constituents of the endosarc commonly consist of a few 

 Navicular or Protococci; but often a greater number of the same are 

 present, and sometimes considerable portions of Oscillaria. In addition, 

 brownish and colorless food-balls and a few oil-like drops may be present. 



Of the young of Amceba verrucosa I have observed individuals range 

 from the 5 ^th of a line in length by the j^th of a line in breath, up to the 

 size of mature forms. 



The four longitudinal lines, originally supposed to be a distinctive 

 character of Amoeba quadriliiieata, though the usual number, are by no 

 means constant, for I have observed them to vary in different individuals 

 from a single one to half a dozen. As the animal grows they appear to 

 become less evident, and ultimately become obsolete or undistinguishable 

 from the many temporary wrinkles of the surface. See figs. 1-4, 8, 9, 

 12-27, 30-32, 37. 



Individuals of the Amcsba terricola of Dr. Greeff* bear a near resem- 



*Arch. mik. Anat. 1866, ii, 299, Taf. xviii, Fig. 1-11. 



