28 Microscopical Besearches on the Conformity of 



although they often project beyond it in the form of small eminences, 

 (According to the recent observations of Rosenthal, the nuclei of the mus- 

 cles, even of an adult, are not wholly effaced.) The muscular substance, 

 properly so called, of the cylinder, is produced by a secondary deposif^^ 

 in the interior of the canal. (The structureless case of small primitive 

 muscular fascicles, which I observed long since in insects, appears to be, 

 says Miiller, the remains of the secondary membrane of the cells.) 



(According to Valentin's last observations {Archiv of Muller 1840), 

 there is to be seen in the blastema of the muscles, at first nuclei, with 

 nucleolules, which soon surrounded themselves with very delicate cells. 

 These cells become elongated and arranged in lines like threads of a con- 

 ferva. On the walls of the secondary cellular membrane, which thicken 

 more and more, longitudinal fibres are produced, and the walls of the 

 cells are absorbed. The muscular fascicle then represents a tube, whose 

 walls, proportionally thick, are formed of longitudinal threads, as trans- 

 parent as glass, and the interior of which encloses thp nuclei of the pri- 

 mitive cells.) 



Each nervous fibre is a secondary ccll^ arising from the union of the 

 primary cells provided with nuclei, Schwann believes that the wliite 

 substance, which enters at a later period into the composition of the 

 white nervous fibre which forms a continuous tube, the ribbon of Re- 

 mack, is a secondary deposit of the internal surface of the cellular mem- 

 brane. This white substance is in fact surrounded by a particular mem- 

 brane without structure, like the primitive muscular fascicles. This mem- 

 brane appears like a narrow transparent border, which is easily distin- 

 guished from the deeper contours of the white substance. This well- 

 marked exterior definition of the boundaries prevents us, says Schwann, 

 from regarding the membrane in question as composed of a cellular tis- 

 sue. Schwann has sometimes seen in the nerves where the white sub- 

 stance is perfectly formed, a cellular nucleus disposed here and there in 

 the edge of the exterior membrane. In the grey nervous fibres, the white 

 substance is not developed. (According to Valentin, the cells of the 

 cerebral substance^ in young embryos, besides the granules they contain, 

 and which will soon multiply, are surrounded by an enveloping mass. 

 The commencing cell forms the nucleus, its nucleus the nucleolule, and 

 the enveloping mass the fundamental mass of the ganglionic globule. 

 VV^hen the cells have formed the nervous fibres, there are deposited on 

 the surface of the latter the nuclei of the cells, cellular fibres, and fibres 

 of cellular tissue.) 



On the walls of the capillary vessels of the larvae of frogs, we see the 

 nuclei of cells at certain distances from each other. They arc situated in 

 the thickness of the wall, or on the inner face of the capillary vessels, on 

 which they often form a prominent point. According to Schwann, the 

 capillary vessels of the embryo are probably formed in the following man- 

 ner : some of the cells of the germinative membrane change into stelli- 

 form cells by the prolongation of their parts. Tlie elongations are ap- 

 plied one against another, become soldered together, the walls are ab- 



