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



The ova of about forty British fishes have been examined, and in most cases the 

 development of the young before and after leaving the egg, as far as possible, followed. 

 The period over which the special observations extended commenced with the work for 

 H.M. Trawling Commission in 1884, when the talented chairman (Lord Dalhousie) placed 

 every encouragement (personal and administrative), and all the facilities in his power 

 for pursuing the subject as thoroughly as time would permit. The experience of former 

 years at St Andrews and elsewhere has been made available, especially in regard to the 

 growth of marine fishes, and to the structural features in the later stages of the salmon. 



The ova examined at St Andrews may be conveniently arranged in two divisions, 

 viz., Pelagic or floating eggs, and Non-Pelagic or demersal eggs. 



Under the former head twenty-three species may be grouped, viz., Long-Rough Dab, 

 Turbot, Plaice, Lemon-Dab, Craig-Fluke, Common Dab, Common Flounder, Sole, Muller's 

 Topknot, Ling, Five-bearded Rockling, Cod, Haddock, Bib, Whiting, Poor Cod, Green 

 Cod, Pollack, Frog-fish, Skulpin, Lesser Weever, Sprat, and Grey Gurnard. Besides the 

 foregoing, the Common Eel and the Conger have been examined ; but their pelagic or 

 demersal character has not been finally determined. 



The non-pelagic ova include at least fourteen species, besides a few doubtful forms of 

 which the ovarian eggs alone have been under consideration. This (demersal) group 

 embraces the Herring, Smelt, Salmon, Trout, Bimaculated Sucker, Wolf-fish, Shanny, 

 Viviparous Blenny, Montagu's Sucker, Lump-sucker, Goby, Armed Bullhead, Cottus, 

 Fifteen-spined and Three-spined Stickleback, Sea Bream, Gunnel, &c, besides the 

 Cyclostome — Myxine. Amongst the doubtful eggs are those of Yarrell's Blenny and the 

 Sand -Eel (Ammodytes tobianus). 



II. The Mature Ovum. 



General Features. — The mature ovum of osseous fishes is generally of comparatively 

 small size, spherical in form, and more or less translucent. Two parts may be distin- 

 guished, viz., a protective external capsule (PI. I. figs. 1-4. zr), and a contained vitelline 

 mass (y), the latter consisting of a globe of food-yolk, with interfused germinal matter. 

 Upon being placed in water, the ova of some species float near the surface and throughout 

 the water ; these, as already pointed out, form the pelagic group; while in other species the 

 eggs sink to the bottom, and form the second group, viz., the demersal or non-floating eggs. 

 The first group exhibit in a striking way the feature characteristic of pelagic structures, 

 viz., a colourless translucency ; while the second or demersal group are less delicate in 

 appearance, and often tinted in a marked manner. Thus the freshly extruded ova of 

 Cyclopterus lumpus are of a brilliant purplish rose, or a subdued green or yellow tint, 

 which soon, however, fades away, and the eggs become more translucent. The ova of 

 the salmon, by their rich orange colour, afford a familiar example of tinted demersal eggs ; 

 while those of many species of Stickleback (e.g., Gastrosteus spinachia) are of a trans- 

 parent amber-tint. Such coloration, as just noted, like the whitish opacity of the ovarian 



