48 



LECTURE I. 



FIG. 9. 



In the following preparation a piece of costal carti- 

 lage, in a state of morbid growth changes are evident 

 even to the naked eye, namely, little protuberances upon 



the surface of the cartilage. Cor- 

 responding to these the microscope 

 shows a proliferation of cartilage- 

 cells, and we find the same forms 

 as in the vegetable cells ; large 

 groups of cellular elements, each 

 of which has proceeded from a 

 single previously existing cell, 

 arranged in several rows, and dif- 

 fering from proliferating vegetable 

 cells only in this that there is 

 intercellular substance between the individual groups. 

 In the cells we can as before distinguish the external 

 capsule, which, indeed, in the case of many cells, is com- 

 posed of two, three, or more layers, and within them 

 only does the real cell come with its membrane, contents, 

 nucleus, and nucleolus. 



In the following object you see the young ova of a 

 frog, before the secretion of the yolk- granules has begun. 

 The very large ovum (Eizelle) (Fig. 10, C) contains a 

 nucleus likewise very large, in which a number of little 

 vesicles are dispersed and tolerably thick, opaque con- 

 tents, beginning, at a certain spot, to become granular 

 and brown. Around the cell may be remarked the rela- 

 tively thin, connective tissue of the Graafian vesicle, 

 with a hardly visible layer of epithelium. In the neigh- 

 Fig. 9. Proliferation of cartilage ; from the costal cartilage of an adult. Large 

 groups of cartilage-cells within a common envelope (wrongly so-called parent- 

 cells), produced from single cells by successive subdivisions. At the edge, one of 

 these groups has been cut through, and in it is seen a cartilage-cell invested by a 

 number of capsular layers (external secreted masses). 300 diameters. 



