552 DEVELOPMENT OF THE SIMPLE TISSUES. BY S. STRICKER. 



I can now discuss but very briefly the development of the 

 muscular fibres. So far as my observations extend in the 

 embryoes of Rabbits, I must support the views of Kemak and 

 those who agree with him, that a muscular fibre proceeds from 

 a cell, which elongates and becomes fusiform, and at the same 

 time increases in thickness; the nucleus then increases, and on 

 its surface appears a mantle of longitudinal strise, which at 

 the same time represents the cortex of a nucleated and granu- 

 lar medullary substance. As soon as this mantle is formed, 

 fibres may also be met with, in which the transverse striae are 

 apparent. Up to this period it appears as if each fusiform 

 cell were undergoing gradual conversion into muscular sub- 

 stance from the periphery towards the centre. It is important 

 to notice that the first traces of muscular substance in the fibre 

 cells constantly appear to be fibrillar. It must, however, also 

 be stated that it is impossible to investigate such fibres in a 

 perfectly fresh condition. When they are removed from the 

 living embryo, they rapidly die, and it is therefore not easy to 

 determine whether the muscular substance is always fibrillar 

 at its first appearance. In regard to the development of the 

 sarcolemma, I must mention that I can discover no reason, from 

 a study of its development, for considering it as a cell mem- 

 brane. On the contrary, I have made observations which render 

 it very probable that the sarcolemma is to be referred to cells 

 which attach themselves to the muscle cells, and ultimately 

 enclose them. For if a teased-out preparation be prepared 

 from a trunk muscle of the foetus of a Rabbit at a time when 

 the muscular fibres are still so imperfectly developed that they 

 are either homogeneous, or are composed of cortex and medulla, 

 it will be found that they lie enclosed in clusters of smaller cells. 

 Moreover we find that more or less strongly projecting nucleated 

 cells adhere to various points of the surface of the fibres when 

 isolated. We may see also how the body of such a cell 

 extends beyond the optical longitudinal section of the fibre 

 as a thin extremely transparent marginal stria, which already 

 presents the aspect of a section of the sarcolemma. With re- 

 gard to the question of what now contributes to form Schwann's 

 sheath ; with regard, further, to the fact that the sheath of 

 Schwann and the sarcolemma are, sometimes continuous 



