490 SUMMARY OF CURRENT RESEARCHES RELATING TO 



blastic, and thinks derived from the yolk, and destined to form the 

 connective and vascular tissues. Eomiti admits the double origin, but 

 maintains that the independent cells are derived from the germinal 

 portion. The cells in the periphery of the mesoderm are derived 

 " from the proliferation of some large cells which have emigrated 

 from the segmented germ, and lie between the primitive layers." 



Histology of the Ovary of Mammals.* — W. Harz finds in the 

 ovary of mammals structures of an epithelial nature, which have the 

 form of massive cords, of canals, or of groups of cells, which are all 

 distinct from the structures of the germinal epithelium. These epi- 

 thelial structures in the ovary can, however, only be derived from one 

 of two sources : they must either' be developed from the germinal 

 epithelium or from the segmental system. It would appear to be 

 certain that the canals and epithelial cords arise from the mesovarium 

 and only pass at a relatively late period into the stroma of the ovary. 

 In some cases, indeed (man, pig) remnants of the structures persist in 

 the mesovarium or in the region of the hilus of the ovary (sheep) ; 

 and this is a conclusive pruof that they are not derived from the 

 germinal eiiithelium. This view is supported by the statement of 

 M. Braun, who has directly observed the passage of epithelial cords 

 and canals from the wall of the glomeruli of the primitive kidneys 

 into the rudiment of the genital organ. In some mammals the 

 structures in question are not always rudimentary, but become exceed- 

 ingly well developed (hare, horse, &c.) ; and between the two condi- 

 tions, presented by the pig and the horse respectively, we have an 

 intermediate arrangement, such as that seen in the cat or the sheej), 

 where cords or cell-groups of epithelial nature are found extending 

 some way into the ovary. 



The author is led to doubt the accuracy of the view which ascribes 

 to these epithelial cords any share in the formation of the membrana 

 granulosa, and he does not believe that the segmental cells have any 

 part in forming the corpora lutea. 



With regard to the mechanism of the migration of the ova Harz 

 believes that some attention must be given to the fact that a primor- 

 dial ovum, before it sinks below the surface of the gei'minal epithelium, 

 becomes overgrown by epithelial cells ; this epithelial investment 

 may perhaps exercise a pressure on the egg-cell, whigh is an agent 

 in the movement. The albuginea appears to have a regulative action 

 in this function of the germinal epithelium, for so long as primordial 

 ova are being actively produced, it is non-existent ; in connection 

 with this we must remember that the albuginea is very poorly supplied 

 with blood-vessels. 



The segmental tubes of the calf and of the cat call to mind the 

 ovarian tubes figured by Pfliiger, and lead to the idea that this 

 author's ovarian tube is in part a development from the segmental 

 system. Where genital rudiments are feebly developed primordial 

 ova may be observed in those segmental tubes which are closely con- 

 nected with the germinal epithelium. 



* Arch. f. Mikr. Anat., xxii. (1883) pp. 374-407 (1 pi.). 



