No abstract

No abstract

The present status of the pure line hypothesis Literature cited. Appendix-Soine important correlation tables. (3) Inheritance in the Asexual Reproduction of Centropyxis aculeata. (4) diverse strains, called "pure lines", "clones", or "biotypes", differing from each other, but each one constant and invariable in its c\"n hereditary constitution. This last idea, that every individual of any given clone is precisely the sane in its genetic make-up as any otVier individual of the same clone, is the basic idea of the pure line concept. As a corollary, it follov/s that all the variations four-d within .a single clone are piirely somatic and not heritable. In this case, it is evident,^.-election working witliin a clone could have no effect. The testing of this hypothesis, then, is of the greatest importance for any general consideration of t'ne mechanism of evolution. This problem has already attracted the attention of numerous investigators. 3ome have com.pletely comfirred the conclusions of Johannsen. Tiie more important of these papers have already been cited. But t?iere are others who have maintained that hereditary variations do occur within clones, and that selection withi.n a clone may have an effect. Pearson (1910), subjecting the data of the earlier pure line workers to a more accurate statistical analysis, found evidence indicating that such inheritance might exist. otout (1915), stocking U915), Middleton (1915), and Jennings (1916) have all succeeded in isolating, by selection, hereditarily diverse strains within single clones. The present paper adds another similar case to this list. Problems. Accepting, as we must, the fact that th.ere do exist, within a single species, diverse strains or races, there are two main problems which claim our attention.

FIVE FIGURESFor 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

No abstract