INTRODUCTION. 7 



searches upon the terminations of the nerves in the tail of the 

 Larvce of frogs (Medic. Zeitung, 1837), I not only saw the beau- 

 tiful cellular structure of the Chorda Dorsalis in these larvae, but 

 also discovered the nuclei in the cells. J. Miillcr 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. Midler 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 larvse, 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 oppor- 

 tunelv 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 larvse 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 sue- 



