up of several simpler compounds not well understood. Nor is it always green, though in that form it occurs most familiarly. Sometimes the true chlorophyl is obscured by some other color, and is nevertheless perfectly functional, physiologically speaking; for instance, a yellow color is particularly common in the lower forms of plants—as in the algæ.
In 1871 Cienkowski boldly announced his conviction that certain yellow cells, which, first pointed out by Huxley, had for some time attracted attention in the substance of radiolarians, were really no part of the animals themselves, but rather veritable algæ living in the animals. Haeckel had previously called them "liver-cells," and when starch was found in them he believed his view confirmed, as it is in the liver of the higher animals that glycogen—a form of starch—is constantly present. The views of Cienkowski made little progress, however, till 1879, when a distinguished morphologist, R. Hertwig, of Jena, who had previously taken sides with Haeckel, adduced reasons which inclined him to the belief that the yellow cells were "parasitic," as Cienkowski had considered them to be.
In the same year (1879) the brothers Hertwig concluded that the so-called pigment-bodies in the tentacles of certain sea-anemones are true algæ—plants, multiplying bydivision. Then followed quickly the paper by Dr. Brandt, referred to at the beginning of this review. His work was extensive, and resulted in a complete confirmation of the observations of Cienkowski and the Hertwigs. He fully believes that the yellow cells are true algae, and was able to prove his points to his own satisfaction. He went, however, a step further, and announced his conviction that all animal chlorophyl is to be considered as located in associated vegetable organisms, which, together with the animal, make up "a partnership of plant and animal life." He unhesitatingly puts Hydra viridis and Spongilla (green variety) in this position, and thus disposes of all "vegetating animals," or animals living like plants endowed with chlorophyl.
In October, 1881, Mr. Geddes visited Naples for the sake of making further studies upon this subject, and in the paper in "Nature," referred to above (and which has been freely drawn upon in preparing this review), he gives a summary account of his work.
He devoted his attention at first to the yellow cells of Radiolaria, and was completely successful in demonstrating in them not only a cell-wall of cellulose and contents made up of protoplasm and nucleus, but he was also able to watch their growth both before and after the death of the animal; and, what was of special interest, he obtained a fair amount of evidence that certain tiny bubbles which in sunlight studded the radiolarians were really made up, in part at any rate, of oxygen. Besides this, he pronounces starch to be invariably present, and completely confirms the observations of Cienkowski and Brandt as to the survival and growth of the yellow cells long after the animal