OF THE VERTEBRATE OVARY. 583 



reaches O'5 mm., a single germinal spot is always present (mea- 

 suring about O'oi mm.), which is absent in larger ova. 



The bodies described by Gegenbaur are now generally recog- 

 nised as germinal spots, and will be described as such in the 

 sequel. I have very rarely met with the condition with the 

 single nucleolus described by Schultz in Torpedo. 



My own observations are confined to Scyllium. In very 

 young females, with ova not larger than 0*09 mm., the germinal 

 vesicle has the same characters as during the embryonic periods. 

 The contents are clear but traversed by a very distinct and 

 deeply staining reticulum of fibres connected with the several 

 nucleoli which are usually present and situated close to the 

 membrane. 



In a somewhat older female in the largest ova of about O'I2 

 mm., the germinal vesicle measures about O'o6 mm., and usually 

 occupies an eccentric position. It is provided with a distinct 

 though delicate membrane. The network, so conspicuous during 

 the embryonic period, is not so clear as it was, and has the 

 appearance of being formed of lines of granules rather than of 

 fibres. The fluid contents of the nucleus remain as a rule, even 

 in the hardened specimens, perfectly clear, though they become 

 in some instances slightly granular. There are usually two, 

 three, or more nucleoli generally situated, as described by Eimer, 

 close to the membrane of the vesicle, the largest of which may 

 measure as much as o - oo6 mm. They are highly refracting 

 bodies, containing in most instances a vacuole, and very frequently 

 a smaller spherical body of a similar nature to themselves 1 . 

 Granules are sometimes also present in the germinal vesicle, but 

 are probably only extremely minute nucleoli. 



In ova of O'5 mm. the germinal vesicle has a diameter of O'I2 

 mm. (PI. 25, fig. 21). It is usually shrunk in hardened specimens 

 though nearly spherical in the living ovum. Its contents are 

 rendered granular by reagents though quite clear when fresh, 

 and the reticulum of the earlier stages is sometimes with difficulty 

 to be made out, though in other instances fairly clear. In all 

 cases the fibres composing it are very granular. The membrane 



1 Compare, with reference to several points, the germinal vesicle at this stage 

 with the germinal vesicle of the frog's ovum figured by O. Hertwig, Morpkologisches 

 Jah;-buch, Vol. in. pi. 4, fig. i. 



