400 NOTES AND MEMORANDA. 



Ova taken from a number of females at Grimsby and on the 

 North Sea showed but little variation^ the usual diameter being 

 I'Ol mm., and the extreme sizes "99 and 1*06 mm. The oil-globule 

 is nearly always •21 mm., but may be as small as "18 mm. Thus the 

 ova of '77 mm., supposed by Wenchebach to be ripe, must have been 

 unusually small if they were really in that condition. 



The yolk is colourless and homogeneous, but the oil-globule in 

 recently spawned ova has a very pale ochreish tint. This is hardly 

 visible unless a great number of ova are together in a vessel, when 

 the globules impart their colour to the whole mass. Under similar 

 conditions the ova of the brill {B. hems) exhibit the colour of a 

 very weak solution of ink, also due to the oil-globules. 



The zona exhibits much the same characters as that of the brill, 

 but the markings due to elevations of the internal surface are less 

 closely set, forming a rather open network, of no regular pattern. 

 They are retained, at all events in artificially fertilized examples, 

 until a late period of development in ovo. The whole structure is 

 less delicate than that of the megrim {Rhombus megastoma) . 



Fertilization does not appear to affect the dimensions ; the peri- 

 vitelline space is small. Unfertilized ova seem to retain their vitality 

 for an unusually long period ; some were successfully fertilized 1 7 

 hours after they were taken from the parents. Sir James Maitland's 

 experiments with the milt of Salmonidee will be remembered in this 

 connection. 



I was only successful in hatching one lot of ova. The larvas 

 began to emerge on the seventh day, but most emerged on the ninth 

 day. None lived for more than a few days after hatching. They 

 were very likely more feeble than those hatched under natural con- 

 ditions, although as the attempt to rear them was made at sea, with 

 plenty of good water available, I do not know why they should have 

 suffered. 



The newly hatched larva measures only 2 14 mm., of which con- 

 siderably more than half is occupied by the yolk. The oil- globule 

 is ventral in position instead of posterior, as seems to be the case in 

 the brill. The marginal fins are narrow, the pectorals remote from 

 the eye, and the whole larva appears less advanced than is usual in 

 Pleuronectids at the time of hatching. 



Both black and coloured chromatophores are present, the latter 

 being the most numerous. In the newly hatched larva they 

 are simple and almost entirely to the head, trunk, and tail, and to 

 the periblast internal to the oil-globule ; but they soon become den- 

 dritic and spread all over the skin, except at the caudal extremity, 

 being less abundant than elsewhere on the yolk-sac. When first 

 visible the coloured pigment is pale yellow, but by the time of 



