OEIGIX AXD MIGEATIOX OF THE GEEM-CELLS IX 

 ACANTHIAS. 



FREDERICK ADAMS WOODS, M. D. 



From the Emhrijologkal Laboratvry of the Harnard Medical School. 



With 14 Text Figukes. 



The dog-fisli liaviiig been used so extensively as a basis for onr knowl- 

 edge of the morphology and development of the genito-urinary system, 

 any further contribution in this department of anatomy can be easily 

 fitted in to larger accounts, such as wq have from the well-known in- 

 vestigations of Balfour, 78, and Semper, 75, who used this and closely 

 allied species in their pioneer genito-urinary researches. 



" Since Semper's time, in 1875,"' to quote from Dr. Minot's Em- 

 bryology, p. 250, " it has come to be more and more generally admitted 

 that the development of the genital glands leads in both sexes through 

 an early stage characterized by the appearance of primitive ova {Ureier, 

 Frimordialeier, ovoblast). The primitive ova are merely enlarged cells 

 of the germinal epithelium (or so-called medullary cords)." 



Balfour gives the following location of primitive ova when first ob- 

 observed, 78: 



'' The primitive ova are confined to the region which extends pos- 

 teriorly nearly to the end of the small intestine and anteriorly to the 

 abdominal opening of the segmental duct. 



" The portion of the mesentery in which the primitive ova are most 

 densely aggregated corresponds to the future position of the genital 

 ridge, but the other positions occupied by the ova are quite outside this. 

 Some ova are in fact situated on the outside of the segmental duct and 

 segmental tubes, and must, therefore, effect a considerable migration 

 before reaching their final positions in the genital ridge on the inner 

 side of the segmental duct."' 



These cells destined to form the ova in the female and probably the 

 spermatozoa in the male are to-day generally considered to be derived 

 from the germinal epithelium of the genital gland. The epithelium 

 itself is a modification of the embryonic peritoneum and its special re- 

 gion is indicated in the drawing of the 19 mm. embryo (Fig. 14 Ur). 



