From the Zoological Laboratory of the Johns Hopkins Uniziersity
FIVE FIGURES
For several years past we have occasionally collected amebae in a brick-yard pond in the vicinity of Baltimore. These amebae are large lobose forms which correspond, a t least superficially, with the ordinary descriptions of Ameba proteus (fig. 1). They feed almost exclusively on living organisms and thrive remarkably well in hay-infusions. When the infusoria in such cultures begin to decline the amebae begin to increase rapidly and frequently become so numerous that the substratum on which they are found appears distinctly grayish; but as the infusoria diminish the amebae decrease in numbers and eventually apparently disappear entirely, but they usually appear again if more hay and water is added so as to induce the infusoria to develop. We have found this to occur in cultures which had been inactive as long as four months. By occasionally adding a little hay and water, we have succeeded in keeping, in ordinary glass dishes, cultures of these amebae for several years. They could, no doubt, be kept indefinitely.
In connection with other work on these amebae we have incidentally observed some remarkable phenomena associated with feeding. Some of these phenomena were of such a nature that it is impossible to account for them on the assumption that movement in ameba is exclusively due to changes in surface tension as is maintained by Butschli ('92), Ryder ('94), Jensen ('05), Verworn ('09) and others, and they seem to indicate that the r81e played by surface tension is far less significant than has 33 THEJOURNAL OF EXPERIMENTAL ZOOLOOY, YOL. 21. NO. 1 f:
C -
Fig. 1 Camera sketches of a rotifer and an ameba which has been feeding on rotifiers: n, nucleus; c, contractile vacuole; f, food vacuole, containing rotifiers; e, eyes; p , pharynx; mm, projected scale.
A Ameba and rotifier showing their relative size under normal conditions. Drawn November 20, 12 m.
It contains one large and two small rotifers, all partially digested and apparently much decreased in size.
Both were attached t o the large one when i t was captured and they were swallowed with it. B Drawn November 20, 12.40 p.m.
C and D Same ameba drawn November 3, 11 and 11.05 am., respectively.
Note that the rotifers in the food vacuoles have apparently become somewhat smaller during the preceding three days. They also became more translucent, but they were apparently still far from being completely digested. Moreover, when the ameba was discovered they were already much smaller than normal, indicating that they had been captured a considerable time earlier (compare with fig. 2e). Thus i t is evident that in this case it would have required much more than three days to digest the rotifers. When the last sketch was made the ameba was active and apparently in excellent condition, but three hours later it was found dead and partially disintegrated. 34
Note the large food vacuole in the ameba.
Only one of the small rotifers is shown in the sketch.
The same ameba showing the three rotifers in the food vacuoles.