FORMS PRESENTED BY CELLS. 41 



Where the cells line the interior of cavities as a single layer, 

 they appear either in the form of plates of different shape 

 (endothelial cells of His), or of cells in which the long axis is 

 predominant (cylindrical epithelial cells) ; or we may meet 

 with various intermediate forms between plates and cylinders. 



The cylindrical cells are not cylinders in a stereometric sense, 

 but are frequently conical, with the base turned towards the 

 cavity, whilst at other times they form cones, from the apex 

 of which a process is given off. Cells may again present the 

 appearance of being as it is termed ramified, or provided with 

 numerous processes (bone cells, corpuscles of the cornea) ; or 

 lastly, they may become extraordinarily elongated as in mus- 

 cle cells. 



A form of cell which must be regarded as quite peculiar, 

 is that which is provided with cilia. The form of the 

 ciliated cell varies to a considerable extent, but the cilia 

 are always limited to one portion of the surface, and con- 

 stantly project with their free extremities into the interior of 

 the cavity of the organ they line. 



The cilia themselves may be of various length, and may on 

 the one hand considerably exceed the long diameter of the cell, 

 as occurs in those lining the renal capsules of some amphibia 

 (Remak,* Duncan) ; and on the other may be so short that they 

 only measure a fraction of the long diameter of the cell ; it is in 

 such cases especially that when at rest they give the appear- 

 ance of a moderately broad hem or border to the cell. Again, 

 not only the length but the thickness of the cilia varies ; thus 

 we find that the cilia on the superficial cells of the egg of the 

 frog, after it has undergone segmentation, can scarcely be per- 

 ceived even when magnified 400 times with a good instrument ; 

 whilst the cilia on the gills of the Anodonta are easily re- 

 cognized near their base with a very low power. 



UNION OF CELLS WITH EACH OTHER. By the treatment of 

 tissues with diluted solutions of nitrate of silver, as suggested 

 by Recklinghausen, we have acquired a knowledge of the 



* Frorieps Notizen, 1845. 



t Wiener Sitzungsberichte, 1867. 



