554< DEVELOPMENT OF THE SIMPLE TISSUES, BY S. STRICKER. 



itself. By careful observation, however, and with good micro- 

 scopic powers, a thin layer of protoplasm may already be dis- 

 tinguished, which is sharply defined on all sides from the large 

 nucleus, and gives origin to the axis cylinder. The axis cy- 

 linder, which at its origin is relatively thick and conical for the 

 most part, becomes attenuated as it passes outwards, without 

 undergoing division, and is directly traceable into a very slender 

 fibril. In this condition it emerges from the cranial cavity of 

 the embryo, and extends to the most remote parts, where it not 

 unfrequently breaks up into a fasciculus of extremely fine 

 fibrils, only clearly visible with Hartnack's No. 15. 



