ON THE DEVELOPMENT OF THE ANIMAL TISSUES. 79 



to remove the surrounding portions. This is said to be Mr. C. M. 

 Topping's plan. 



Diamonds of good quality for these purposes may be obtained from Mr. 

 Ellis, Goswell Street Road. The price of a good cutting diamond, 

 for ordinary purposes, is about fourteen shillings, that of a scratching 

 one, a guinea. 



The Microscopical Society of London possesses a machine for cutting 

 glass for slides of any desired size, which may be made use of by its 

 members, on application to the Secretary. Mr. Drake of Jermyn 

 Street is also in possession of a similar instrument, and supplies strips 

 of glass to order. 



XVI. ON THE DEVELOPMENT OF THE ANIMAL TISSUES.* 



By Professor Muller. 



MODERN Vegetable Physiologists have for some time arrived at the result 

 that the different tissues of plants, such as cellular tissue, woody fibre, 

 ducts, and spiral vessels, are all originally developed from cells. The 

 mode of formation of these cells has been explained by Schleiden.t He 

 has shown that they are produced from the " nuclei " of Robert Brown, 

 and hence he calls these bodies " cytoblasts" [KVTOQ a cell, pXaaroQ a 

 germen] . The cy toblast is generally of a yellowish colour, and inter- 

 nally of a granular structure. In its interior Schleiden has detected a 

 second nucleus (nucleolus), called by him the nucleus corpuscle, which 

 sometimes resembles a mere spot, at other times a hollow globule. The 

 cytoblasts are developed in a mass of mucous granules contained within 

 previously existing cells. As soon as they have attained their full size, 

 a delicate transparent vesicle rises upon the surface of each. This is 

 the young cell, which at first bears the same relation to the flat nucleus 

 as the watch-glass bears to a watch. When the cell has increased in 

 size, the cytoblast appears merely as a solid body included in the wall of 

 the cell. The layer which now covers the cytoblast on the side towards 

 the interior of the cell is extremely delicate indeed, seldom to be recog- 

 nized by the eye and it soon becomes wholly absorbed, while the cyto- 

 blast itself disappears at the same time. The newly developed cells lie 

 free in the cavity of the parent cell, and, as they grow and exert reci- 

 procal pressure against each other, assume the polyhedral form. 



* From Miiller's Elements of Physiology, translated by Dr. Baly, p. 1641. 

 f Miiller's Archives, 1838, p. 137. 



