The correctness of this interpretation, which is in reality mainly a statement of observations, is proved by the two following groups of facts. The older observers had already noticed that the unfertilized eggs of the sea urchin when lying in sea water will die after a day or more, and that occasionally such eggs show nuclear division or even the beginning of cell division shortly before disintegration sets in. The writer has studied this phenomenon in the unfertilized eggs of _purpuratus_ and found that only the eggs of certain females show this cell division before disintegration and that the cell division is preceded by an atypical form of membrane formation; the eggs surrounding themselves by a fine gelatinous film comparable to that produced in the egg of _Arbacia_ by a treatment with butyric acid. It is difficult to state what induces the alteration of the surface in the eggs that lie so long in sea water. It may be due to the CO₂ formed by the eggs--since we know that CO₂ may induce membrane formation--or it may be due to the alkalinity of the sea water or to a substance originating from the jelly surrounding the eggs. It was found that if such eggs are kept without oxygen their disintegration (and cell division) will be delayed considerably. The presumable explanation for this is that the lack of oxygen prevents the internal changes underlying cell division and thus prevents the disintegration of the egg. The direct proof that an egg in the process of cell division is more endangered by abnormal solutions than an egg at rest has been furnished by numerous observations of the writer. He showed in 1906 that the fertilized egg of _purpuratus_ dies rather rapidly in a pure m/2 NaCl or any other abnormal isotonic solution, while the unfertilized egg can live for days in such solutions.[99] In a series of papers, beginning in 1905, he showed that the fertilized egg will live longer in hypertonic, hypotonic, and otherwise abnormally constituted solutions when the cell divisions are suppressed by lack of oxygen or by the addition of KCN or of chloral hydrate.[100] It is thus obvious that coincident with the changes underlying nuclear division or cell division alterations occur in the sensitiveness of the egg to salt solutions of abnormal concentration or constitution, _e. g._, NaCl+CaCl₂ isotonic with sea water, hypertonic, or hypotonic solutions. [99] Loeb, J., _Biochem. Ztschr._, 1906, ii., 81. [100] Loeb, J., _Arch. f. d. ges. Physiol._, 1906, cxiii., 487; _Biochem. Ztschr._, 1910, xxvi., 279, 289; xxvii., 304; xxix., 80; _Arch. f. Entwcklngsmech._, 1914, xl., 322.