of the Fishery Board for ScotlaiuL 



93 



If we now compare the fully mature ovaries of a Teleostean whose eggs 

 are pelagic with those of one whose eggs are demersal, a striking difference 

 will be perceived. In the latter, as already indicated, the eggs which are 

 shed are developed equally ; they grow gradually until they reach a 

 certain size, practically uniform in a given species, they become more 

 pellucid or semi-translucent, and are then expelled. ]>ut in species with 

 pelagic eggs, examination of the ovary reveals the presence of large, clear 

 eggs of crystalline transparency, scattered throughout its substance, 

 presenting a marked contrast both in size and appearance to those 

 around them which are whitish, opaque, and smaller. These are 

 the mature ova ready to be shed and fertilised. They have burst 

 through their follicles, they gradually accumulate in the lumen of the 

 ovary, and are normally expelled iu small quantities at a time."^ It is 

 important to observe that extremely few eggs of intermediate size or 

 charactei' are to be found between the opaque ones and the large trans- 

 parent ones. The proportional number of the transparent eggs 

 present in the ovaries depends upon the period in relation to the 

 beginning or end of oviposition. At the commencement of spawning, 

 very few are present. The proportion increases as the spawning proceeds, 

 and towards the end the cavities of the ovaries are distended almost 

 exclusively with the clear mature eggs. 



The Free Ovarian Fluid. 



Little attention has hitherto been given to the free fluid which is found 

 in the ovaries of Teleosteans bathing the lamellae and the mature eggs. It 

 has generally been regarded (1) as a lubricant to facilitate the escape of 

 the eggs during oviposition ; (2) in certain forms as a cementing substance 

 to bind the deposited eggs to one another or to foreign bodies. Among 

 attached or adherent demersal eggs, adhesion is sometimes effected by a 

 special modification of the cortical part of the egg-membrane, sometimes 

 by the stickiness of the outer surface, and sometimes by the hardening of 

 the fluid which bathes the eggs and is expelled with them. In another 

 group the eggs are imbedded in a mucoid substance which causes them to 

 float, as in Scorpcena,'^' Fierasfer^X and Lophius piscatorius.§ I have 

 shown elsewhere (p. 127) that the mucoid matrix that surrounds the eggs 

 in Lophius is secreted by specially modified epithelium. In species pro- 

 ducing isolated pelagic eggs the ovarian fluid which is expelled with the 

 eggs when they are shed is watery; it mingles with the sea water and dis- 

 appears. In immature ovaries the quantity of free fluid present is very 

 small, just sufficient to keep the surfaces of the lamellte Avetted, but in 

 those in which spawning has begun the quantity is considerable; and as 



* It is sometimes supposed that the female sheds her pelagic eggs at random, and 

 that fertilisation is to a large extent a matter of chance ; but this is not the case. One or 

 more males are in close attendance and impregnate the eggs as they escape in small 

 quantities. 



t Hoffman. Zur Ontogenie der Knochenfische. Verhandel. der KoninkL Akad. 

 van Wetensch. Deel. 21, p. 17, 1881 ; Raffaele, Le Uova gallegianti e le larve del 

 Teleostei nel Golfo di Napoli. Mittheil. aus der Zool. Stat, zu Neapel, Bd. viii., 1888. 



+ Emery, Fierasfer. Studi intorno alia sistematica, I'anatomia e la biologia delle 

 specie mediterrauee di questo geuere Fauna and Flora des Golfes von Neapel. 1880. 



§ Agassiz and Whitman. The Development of Osseous Fishes. Mem. Mus. Comp, 

 Zool. Harvard College, xiv., No. i., Part ii. 1889. 



