108 MALCOLM LAURIE. 



The Ovary and Ovarian Egg. 



The ovary consists, as is well known, of three longitudinal 

 tubes connected by transverse anastomoses, so as to form eight 

 quadrilateral meshes. The oviducts arise from the lateral 

 angles of the two foremost meshes and run forward to open 

 together on the genital operculum. The ovary appears to be 

 embedded in the liver, the chief mass of which lies dorsal to 

 it ; this is not really the case, for, though lobes of the liver 

 pass through the meshes of the ovarian network they do not 

 unite on its ventral side. Both the longitudinal and transverse 

 tubes bear ova, which project from their outer surface as 

 oval bodies each attached by a short pedicle and measuring 

 when ripe about 1*2 mm. in length and '83 mm. in breadth. 

 Ova in all stages of development are present on the ovarian 

 tubes at the same time, and there are in addition the corpora 

 lutea (v. p. 111). 



The microscopic structure of the ovarian tubes is shown in 

 PI. XIII, fig. 2. They are there seen to be formed of two 

 layers surrounding an irregular lumen. The outer layer, o. I., 

 which is purely skeletal in function, consists of irregularly 

 polygonal cells, with circular nuclei and strongly marked cell 

 outlines. The contents of these cells are highly refractive. 

 Towards the inside of this layer the cells become flattened 

 so as to form a distinct, cellular, limiting layer. The inner 

 layer, which surrounds the lumen of the tube, is formed of 

 very long and thin columnar cells, with oval nuclei and clear, 

 faintly granular protoplasm. The nuclei are for the most part 

 confined to a central zone, leaving a large part of the outer 

 and a smaller part of the inner ends of the cells clear. It is 

 from this inner layer of cells that the ova and their follicles 

 are formed ; it is, in fact, the germinal epithelium. 



The first sign of the formation of an ovum is that one of 

 the cells of the inner layer of the ovarian tube begins to 

 increase in size (fig. 1, ov.). It contains finely granular 

 protoplasm, a large and distinct oval nucleus, and a darkly 



