694 PROFESSOR W. C. M'INTOSH AND MR E. E. PRINCE ON 



accomplishes fertilisation."" He, however, states that the extrusion of polar bodies, the 

 disappearance of the nuclear spindle, and the aggregation of the germinal area may 

 take place independently of impregnation. Kingsley and CoNNt describe and figure 

 a polar globule in the egg of the cunner apparently after maturation. The globule 

 appeared in the centre of the aster, and passed through the micropyle. List recently 

 does the same in Crenilabrus pavo, the body being globular at seven minutes and rod- 

 like at thirty minutes.! Ryder noted in the ovum of Gadus morrhua a minute 

 granular papilla projecting from the early germ, and looked upon this as representing the 

 polar cells derived from the germinal vesicle (No. 141, p. 477). In Trigla gurnardus, 

 twenty-five minutes after the addition of sperms, a somewhat cylindrical nuclear body 

 has been observed in the superficial protoplasm (PL I. fig. 17, a). It exhibited very 

 slow amoeboid movements, and five minutes after it was first noted it had shortened 

 and contracted in the mid-portion as if dividing into two — a wide granular border 

 extending round it (PI. I. fig. 17, 6). Three minutes later the two separating parts 

 closely approached, and the body became still more contracted and compact — the 

 granular margin also becoming less (PI. I. fig. 17, c) ; but the median cincture was still 

 plainly marked ten minutes later (PI. I. fig. 17, d). A side view of a similar structure 

 in another ovum exhibited two spherical nuclear bodies enveloped in a vase-shaped mass 

 of protoplasm, and from the centre of its wide upper surface radial striations diverged 

 (PI. I. fig. 17, e). No similar appearance has been observed in other pelagic ova seen by 

 us. Mr Cunningham was more fortunate with the ovum of Plevronectes cynoglossus, 

 and he describes a polar globule in this species. § 



The more obvious features in the living ovum after fertilisation are — (1) The 

 meridional streaming of the cortical protoplasm to the animal pole. (2) The formation, 

 or, in certain forms, the visible increase in the size of the blastodisc, and its assumption of 

 a more definite contour. (3) The disappearance of the minute clear vesicles which stud 

 the entire cortex of the vitellus, probably as a consequence of the transference of the 

 protoplasm to one pole — by which they are carried to the region of the disc. In many 

 forms a change in the optical appearance of the yolk is seen. Ransom noticed this, and 

 says that the increased clearness and translucency of the yolk is in part due to distention 

 and greater transparency of the enveloping layer (No. 127, p. 458); indeed, the whole 

 ovum after fertilisation assumes a brighter and more tense appearance. Finally (4), a 

 space slowly becomes apparent between the vitelline globe and the inner surface of the 

 zona radiata, so that the egg-contents are no longer closely applied to the capsule, as in 

 the unfertilised ovum. 



Probably the foregoing features mark the fertilised condition in all Teleostean ova ; 

 but there are many forms in which, for various reasons, they cannot readily be discerned. 



* This closure of the micropyle is perhaps incomplete, as the subsequent formation of a perivitelline space is 

 due to the entrance of water in the main through the micropyle, though it may also enter by the general surface, 

 t Loc. cit., footnote, p. 190. J Op. cit., p. 597, fig. ii. d. 



§ Op. cit., p. 131. 



