INTRODUCTION.
searches upon the terminations of the nerves in the tail of the Larvae of frogs (Medic. Zeitung, 1837), I not only saw the beautiful cellular structure of the Chorda Dorsalis in these larvee, but also discovered the nuclei in the cells. J. Müller had already proved that the chorda dorsalis in fishes consists of separate cells, provided with distinct walls, and closely packed together like the pigment of the Choroid. The nuclei, which in their form are so similar to the usual flat nuclei of the vegetable cells that they might be mistaken for them, thus furnished an additional point of resemblance. As however the importance of these nuclei was not known, and since most of the cells of mature plants exhibit no nuclei, the fact led to no farther result. J. Müller had proved, with regard to the cartilage-corpuscles discovered by Purkinje and Deutsch in several kinds of cartilage, from their gradual transition into larger cells, that they were hollow, thus in a more extended sense of the word, cells; and Miescher also distinguishes an especial class of spongy cartilages of a cellular structure. Nuclei were likewise known in the cartilage-corpuscles. Miiller, and subsequently Meckauer, having observed the projection of the cartilage-corpuscles at the edge of a preparation, it became very probable that at least some of them must be considered as cells in the restricted sense of the word, or as cavities inclosed by a membrane. Gurlt also, when describing one form of permanent cartilage, calls them vesicles. I next succeeded in actually observing the proper wall of the cartilage-corpuscles, first in the branchial cartilages of the frog’s larvae, and subsequently also in the fish, and also the accordance of all cartilage-corpuscles, and by this means in proving a cellular structure, in the restricted sense of the word, in all cartilages. During the growth of some of the cartilage-cells, a thickening of the cell-walls might also be perceived.
Thus was the similarity in the process of vegetation of animal and vegetable cells still further developed. Dr. Schleiden opportunely communicated to me at this time his excellent researches upon the origin of new cells in plants, from the nuclei within the parent-cell. The previously enigmatical contents of the cells in the branchial cartilages of the frog’s larve thus became clear to me; I now recognized in them young cells, provided with a nucleus. Meckauer and Arnold had already found fat-vesicles in the cartilage-corpuscles. As I soon afterwards suc-
