EMBRYOLOGY. 1 



Growth of the Ovum in the Fowl. 2 — Prof. M. Holl, of Gratz, 

 has made a detailed study of the formation of the membranes, acquisi- 

 tion of the yolk and change in the character of the nucleus of the hen's 

 egg, while in the ovary. 



In the chick just hatched the ova form " nests " or clusters of naked 

 cells, each about 14 p thick, beneath the germinal epithelium and 

 surrounded by the connective tissue stroma of the ovary. Each ovum, 

 when about 20 ft thick becomes enveloped by a delicate tunica adven- 

 titia that is really formed by some of the stroma cells flattening 

 themselves out around the ovum ; it is thus a product of the stroma, 

 not of the ovum, though it is usually called the "vitelline" membrane. 



Later the " follicular epithelium," so called, is formed around the 

 ovum by the arrangement of spindle shaped stroma cells in a single 

 layer about the ovum. The author would call this second stroma 

 membrane the granulosa. 



These epithelioid cells increase so that the follicle is made up of 

 several layers. External to it a thin membrana propria is formed bv a 

 few flat stroma cells. Finally the stroma itself is arranged in a system 

 of concentric fibres and cells, external to the three membranes it has 

 formed. The ovum and its fellow epithelial cells are thus excluded 

 from any part in the formation of the egg membranes. 



The large central nucleus of the ovum is at first central, but makes 

 two successive migrations towards the surface of the cell, becoming 

 flattened on one side and applying this side close against the tunica 

 advent&a, when it takes up its permanent position in the ripe egg. 

 [regularities in its contour are regarded, not as pseudopodia, but as 

 artificial products. The nuclear net-work of chromatin has at first 

 a fine mesh, but undergoes complex changes leading to its breaking up 

 into minute granules, which are distributed throughout the nuclear 

 substance. 



The body of the ovum at first presents a wide-meshed system of 

 non-staining material : this is then replaced by a fine-meshed system 

 of staining material radiating out from staining centers, the dotterkern, 

 next the nucleus. This mesh-work becomes finer and finer and its 

 ; Hopkins University. 



