24 Microscopical Besearches mi the Conformity of 



on its internal surface the germinating vesicle, with the germinativc spot. 

 If the germinative vesicle be a young cell, developed in the interior of the 

 vitelline cell, it is probably the most essential element of the embryo j but 

 if this vesicle is the nucleus of the vitelline cell, it loses its importance ; 

 and, judging from the analogy with the greater part of cellular nuclei, it 

 should be at a later period totally absorbed, or rather still continue to 

 exist for some time in a rudimentary state, without constituting any thing 

 essential. The solution of this question cannot yet be attempted. 



The vitelline globules of the t.gg of birds consist of cells of two sorts ; 

 tho vitelline globules of the vitelline cavit}', of the vitelline canal and of the 

 nucleus, of the cicatricule (Hahnentritt^ inclosing a still smaller globule. 

 The other cells are larger and contain a granular matter; water makes 

 them burst, and their contents are scattered on the outside. At first the 

 young vitellus contains only the vitelline cavity with its cells; the true 

 vitelline substance does not yet exist. 



In the somewhat larger ovulas of the ovary, a layer of a yellow substance 

 exists around the cells, itself surrounded by a bed of cellular matter. 

 The yellow matter of the vitellus is then formed between a membranous ex- 

 ternal layer of cells and the internal cells. The lenticular germ is com- 

 posed of globules of unequal size having granular contents. The germ of 

 an egg which has been sat on four hours still contains these globules. In 

 about eight hours the external layer appears, formed of very pale cells, 

 without a nucleus, among which are found globules of the germinative 

 membrane. 



In an egg of sixteen hours, the serous leaflet is formed of cells, some of 

 which contain a nucleus, and one or two minute nuclei (nucleolulcs). 

 They contain, besides, a liquid and very small grains, having a molecular 

 movement. These cells, the nucleus of which was observed by Valentin, 

 soon assume the polyhedral form. The mucous leaflet is composed of 

 cells, with a transparent liquid and grains. These cells, the outlines of 

 which are usually of a deep colour like those of the cells of the vitelline 

 cavity, lie loosely in the midst of an intercellular substance, which con- 

 stitutes their cytoblastema. The first rudiments of the embryo are com- 

 posed in part of small cells without a nucleus, in part of pale cellular 

 nuclei, inclosing nucleolules. 



M. Schwann divides the tissues of the animal organism, in respect to 

 their original and cellular composition, into five classes. These are, 1*^, 

 independent and insulated cells, swimming in liquids, or simply situ- 

 ate near each other and moveable ; 2d, independent {sclbstandig) cells 

 strongly adhering to each other so as to constitute a tissue ; 3rf, tissues in 

 which the walls, but not the cavities of the cells, run into one another; 

 4th, fibrous cells, elongated in one or more directions, in order to form 

 fascicles of fibres ; 5th, cells in which the walls and the cavities are con- 

 founded with each other. 



To the FIRST CLASS belong the corpuscles of the blood, the vesicular na- 

 ture of which Schultz has demonstrated, whose nucleus continues resting 

 against the walls, when they are distended by water, as M. Schwann has 



