222 Part III.— Thirteenth Annual Report 



number are also discharged by the ripe lemon dab. The quantity of ripe 

 eggs which issue from a torsk is about as large in proportion as in a cod, 

 yet the testes of the two differ much in size. 



The egg of the long-rough dab, on issuing from the oviduct, is beauti- 

 fully translucent (PI. VI. fig. 1), and measures from 1*0668 mm. to 

 1-1430 mm. The capsule {zona radiata) clings somewhat closely to the 

 contained yolk, and is wrinkled all over — quite as much as in the lemon- 

 dab. The perivitelline space is small, and thus differs from the condition 

 as ordinarily seen in the tow-nets. As a rule, the yolk or egg proper has 

 a diameter of 1*0668 mm., while the capsule has a diameter of 1*1430 

 mm. When placed in sea-water, and whether fertilized or not, a gradual 

 change takes place in the perivitelline space, so that next morning — that 

 is, in 12 hours, the diameter of the capsule is from 1*7907 to 1*8669 — pro- 

 bably by the imbibition of water, as in the case of desiccated eggs, while 

 the diameter of the egg proper in the centre remains nearly the same 

 (PI. VI. fig. 2). This distention removes many of the wrinkles from 

 the surface, but not all, since these were visible in almost every example 

 up to the period of hatching. Many of the eggs had groups of minute 

 fatty granules dotted all over the yolk, as shown in the figure. Next day 

 (22nd March), at 12.30, considerable progress had been made (PI. VI. 

 fig. 3), the disc being in the mulberry condition, the cells of the blasto- 

 derm being often prominent, and at 5.40 p.m. much more finely divided. 

 The minute granules of oil occur over the yolk, beneath the proto- 

 plasmic investment (PI. VI. fig. 4), and they appeared to be fewer next 

 day, so that probably they were gradually used up in the progress of 

 development. The minutely cellular disc (PI. VI. fig. 5) presents an 

 inward curvature at its edge, which is not quite regular — from the 

 occurrence of minute projecting cells. The disc does not always occupy 

 the centre of the yolk under examination. Occasionally a group of large 

 oleaginous globules lies under the developing disc — not at the upper- 

 most pole of the egg. 



On the 24th, the embryo was outlined — with the optic enlargements 

 (PI. VI. fig. 6). The blastopore in some was almost closed (PI. VI. 

 fig. 7), and Kupffer's vesicle was represented by a few granules or minute 

 vesicles. The notochord formed a pale streak extending forward to the 

 middle of the trunk, and the margins of the body were faintly indicated. 



Next day the blastopore had closed, and Kupffer's vesicle was large 

 (PI. VI. fig. 8). Numerous muscle-plates had formed, and the noto- 

 chord could be traced forwards almost to the head. On each side a 

 delicate cellular border stretched backward outside the muscle-plates. 

 The granules had now disappeared from the surface of the yolk. 



On the 26th March, the embryo resembled Ml Holt's fig. 58, PI. VII.,* 

 and traces of blackish pigment appeared along the body, — best seen by 

 placing white paper beneath the specimens. Besides, there are in some 

 the pale precursors of the pigment-specks, which appear blackish by trans- 

 mitted light. The notochord was visible throughout, the lenses in some 

 were faintly indicated, and the otocysts appeared as elongated thicken- 

 ings with a longitudinal slit, as in the green cod.f The heart was also 

 distinct. The zona was thin, and readily ruptured even when the egg was 

 carefully lifted. 



The following day the blackish pigment formed dark bands, especially 

 when viewed on a white surface, and the next day a faint yellowish tint 

 was visible under a lens. The tail formed a blunt knob projecting 

 beyond the yolk. 



* On the Eggs, larval and post-larval stages, of Teleosteans. Trans. Roy. Soc. 

 Dub. , v. 



t Twelfth Annual Report Fishery Board for Scotland. Pt. iii. p. 219, PL ii. fig. 8. 



