50 PROTOPLASM. 



fully-formed living beings, may be well studied in the simple 

 tissue which forms the external covering of the body, and 

 is prolonged in a modified form into the internal cavities. 

 If a thin section be made perpendicularly through this, 

 down to the tissue which contains the nerves and blood- 

 vessels upon which it rests, the appearances represented 

 in PI. IV, fig. 12, will be observed. 



In the first place, it will be remarked that in equal bulks 

 of the tissue there is a larger quantity of germinal matter in 

 the lower part, a, which is close to the vessels, than in the 

 upper part, <:, which is a long distance from the nutrient 

 surface, and that the converse is the case as regards the 

 formed material which gives to this tissue its properties 

 and physical -characters, Secondly, it will be noticed that 

 the individual masses of germinal matter increase in size 

 till they arrive at about half way towards the surface, fr, while 

 from this point to the surface they diminish, c; and thirdly, 

 that the distance between them increases on account of the 

 increased formation and accumulation of formed material. 

 By the time the cells have reached the surface, the distance 

 between the masses of germinal matter is reduced again, by 

 the drying and condensation of the formed material. 



The changes which each individual cell or anatomical 

 unit passes through may now be considered. At the deep 

 aspect near the nutrient surface are masses of germinal matter 

 embedded in a soft, mucus-like, and, as yet, continuous 

 formed material, a. The masses of germinal matter divide, 

 and each of the resulting masses becomes invested with a thin 

 layer of the mucus-like matter. In this way, the elementary 

 parts or cells multiply in number, to compensate for 



