VOGT'S ACCOUNT OF IT. 119 



Besides these three modes of cell-development, however, Henle re- 

 cognises, with Schwann and other physiologists, another plan in which 

 simple cells are developed, independent of a pre-existing nucleus ; ex- 

 amples of this are seen in the chorda dorsalis of fish and reptiles, as 

 Schwann pointed out, and in cryptogamic and many higher plants, in 

 which a single minute spherule first appears, and this soon becomes a 

 distinct vesicle, rapidly grows, and is eventually extended into a cell. 



The results of investigations by Vogt,* on the development of fishes 

 and reptiles, also tend to shew the occurrence of at least three distinct 

 forms in which the development of cells may take place. In one of 

 these forms the cells appear to owe their origin to a pre-existing nu- 

 cleus, but in the two others they appear to originate independently of a 

 nucleus. 



As already stated, Vogt entirely agrees with Henle in his view of the 

 unimportance of the nucleolus in the process of cell-formation. In by far 

 the majority of cells in young Batrachians and fishes nucleoli were entirely 

 absent ; and in the few in which they existed, as the cartilage-cells of 

 Batrachians, and the embryonic-cells of the salmon, they appeared to be 

 structures of later formation, occurring as simple vesicles which gradually 

 enlarged into cells apparently at the expense of the nucleus, which by 

 degrees entirely disappeared. In no case did they appear to constitute 

 the first stage in the development of cells out of the cytoblastema in 

 the manner described by Schleiden and Schwann. The nucleus, however, 

 appears to be an almost invariable constituent of the cell at whatever 

 period of its life it be examined. But the relation, in point of time, 

 which its development bears to the development of the cell, was found by 

 Vogt, as by Henle and others, to vary in different cases. In one form of 

 cell-development, namely, the production of the cortical cells of the yolk 

 in the toad, the nucleus precedes, and evidently gives rise to, the for- 

 mation of the cell. In another form, which, as shewn by Henle, is well 

 illustrated in the chorda dorsalis of fish, the cells originate without the 

 intervention of nuclei, which only make their appearance after the cells 

 are fully formed. In the third form, the cell and its nucleus seem to be 



hand, Bruch (Henle and Pfeufer's Zeitschrift, b. iv. p. 50) appears to agree with Henle, for 

 he states that the large granular corpuscles frequently met with in cancerous growths, are 

 formed by an aggregation of granules, within which a nucleus is shortly formed, and the 

 whole then becomes surrounded by a cell- wall. Luschka (Entwickelungs-geschichte der 

 Formbe stand theile des Eiters und der Granulationen. Freiburg. 1845.) also agrees with 

 Henle, in believing that the exudation-corpuscles in inflammatory products are formed by 

 the grouping together of numerous minute granules, around each heap of which a cell-wall is 

 then developed, while a nucleus shortly afterwards makes its appearance in the midst. But 

 he also believes that the corpuscles thus formed constitute only an early stage in the develop- 

 ment of pus-corpuscles, into which they are afterwards changed by the absorption of some 

 of their granular matter, and consequent diminution in size. 



* Entwickelungs-geschichte der Geburtshelferkrote, 1842, pp. 118 27. 



