OVAllY AND OVARIAN OVA IN CERTAIN MARINM FISHES. Ill 



geneous mass of transparent almost unstained yolk surrouiuled 

 by a thin envelope of stained protoplasm. The latter contains 

 numerous vacuoles, and its inner surface is very uneven; but I 

 have failed to detect in it any structures representing the 

 nucleus of tlie ovum, which ought to be present in it some- 

 where, and which is distinct enough in the nearly ripe eggs in 

 the same sections. The oil globules, one or more in number, 

 are generally visible just within the protoplasmic envelope. 



Sections of a portion of the ovary of a brill preserved in 

 chromic acid 5 per cent., on September 29th, show an early 

 stage in the development of the eggs for the next spawning 

 season. The largest eggs are '3 mm. in diameter, and are in a 

 condition somewhat more advanced than that of the turbot's 

 egg represented in fig. 10, which is only "17 mm., and similar 

 to that of the gurnard's egg represented in fig. 7. There is in 

 these eggs a broad inner layer of rather large oil globules, and 

 a narrower external zone containing minute yolk granules. 



Although the eggs of the mackerel, like those previously 

 considered, have a single oil globule and homogeneous yolk, I 

 have not seen any indication in them of the presence of scat- 

 tered small oil globules before the commencement of yolk 

 formation. I examined several mackerel 12 to 13 inches in 

 length at Lowestoft, on October 8th, and although they were 

 evidently mature fish which had spawned the previous season 

 (May and June), under the microscope all the eggs were yolk- 

 less, and quite transparent, without any refringent globules. 



On April 27th, 1896, I examined the ovary of a large 

 mackerel in London. This ovary was much enlarged and 

 approaching the ripe condition, but had not begun to dis- 

 charge its ova. Microscopic examination in the fresh condi- 

 tion showed that the majority of the eggs were much advanced 

 in development. They were full of spherical yolk globules, 

 and in the central region could be seen in many the oil of the 

 egg already fused into one large globule. In younger and 

 smaller eggs, a central more opaque zone contrasted with an 

 outer more translucent, as in the eggs of the gurnard, but 

 there were no transparent eggs with separate scattered oil 



