THE ORIGIN OF THE DEFINITIVE OVA 15 



transplantation, (4) the irradiation of ovaries with x-rays, 

 (5) hypophysectomy, (6) the injection of gonad-stimulating 

 hormones and (7) the transplantation of embryonic gonad 

 rudiments. 



Bilateral ovariectomy has been extensively employed in 

 order to determine whether ovarian tissue and eggs can be 

 derived from somatic cells. It is a common experience that 

 ovariectomized animals apparently regenerate ovarian tissue 

 some time after the operation. Thus Davenport (1925) 

 observed as many as 64 per cent of bilaterally ovariecto- 

 mized mice with apparently functional ovarian tissue ap- 

 pearing within a few weeks to several months after the 

 ovariectomy. Such data may be explained as due either to: 

 (1) regeneration of germinal tissue de novo from somatic 

 cells or (2) the presence of accessory gonadal tissue distinct 

 from the ovary and not removed during the operation or 

 (3) the incomplete removal of ovarian tissue so that frag- 

 ments remaining hypertrophy and attain dimensions suf- 

 ficient to permit the manifestation of ovarian function. If 

 the first alternative is accepted then it follows that neither 

 germinal epithelium nor, presumably, primordial germ cells 

 are necessary for the production of ova. The two latter 

 alternatives exclude the first but scarcely affect the problem 

 of origin via germinal epithelium or primordial germ cell 

 though careful observation of the process of hypertrophy 

 may yield pertinent data. Even if the first alternative is 

 acceptable and may thus very well settle the ghost of germ- 

 plasm continuity, it does not necessarily inform us about 

 the normal process of egg production. 



In rodents accessory gonadal tissue is rarely, if ever, 

 present. On the other hand, it is known that fragments of 

 ovarian tissue, remaining after incomplete extirpation of 

 the ovaries, will hypertrophy to such a remarkable degree 

 that a completely normal ovary will be reestablished from 

 which fertilizable ova are liberated (c/. Haterius, 1928; and 

 Pincus, 1931). Furthermore it is quite possible to fail to 

 extirpate small fragments of the irregularly lobed encap- 



