444 Mr. E. E. Prince on the 



and more impressed upon naturalists, that the assertion of 

 generality throughout a class or phylum of organisms for a 

 phenomenon observed only in two or three, or even more 

 members of that class, is an exceedingly risky proceeding"*. 

 Each species has been studied separately and continuously in 

 the laboratory, and much material has been accumulated, 

 which has yet to be exhaustively worked out, and the present 

 paper is chiefly of the nature of a preliminary account. 



Sjjermatozoa. 



The spermatozoa of the diflferent species present no special 

 features and are not readily distinguished from each other. 

 They exhibit, as usual, an enlarged portion or head, which is 

 almost perfectly spherical, with a smooth, refractive, cortical 

 portion and a central translucent part. The vibratile fila- 

 ment, or " tail," is very long, delicate, and homogeneous. 

 They issue from the fully developed male as a whitish fluid, 

 of a rich creamy consistency, and they become diffused very 

 rapidly in sea-water. A large quantity of milt is produced, and 

 it is often expelled with great force. The vitality of the 

 spermatozoa is considerable ; a small quantity exposed upon 

 a slide for three hours exhibited active movements at the 

 end of that time. 



The Ovarian Ovum. 



When approaching maturity the ovum gradually loses the 

 opacity which characterizes it for some time after protrusion 

 from the ovarian stroma. The capsule is disproportionately 

 thick and very pliant ; but it is structureless and destitute of 

 the radiating canals or striee seen in many ova. Minute 

 spherules and refrangible particles are abundant in the fluid 

 contents, and the vesicula germinativa is comparatively large 

 and usually shows a very distinct nucleolus. The intra- 

 ovarian eggs do not ripen simultaneously, and in T. gur~ 

 nardus especially few ova appear to mature at the same time, 

 so that the spawning-process would appear to be protracted 

 and intermittent, less so in the Gadidas and still less prolonged 

 in the Pleuronectidge. 



The Mature Ovum. 



The mature ovum is more or less spherical, and when 

 healthy has an almost crystalline transparency. It exhibits 

 (1) a deutoplasmic globe, chiefly food-yolk, homogeneous and 

 colourless, and destitute of large oil-globules, save in the 

 case of T. gurnardus^ which possesses a single spherical oil- 

 * Quart. Journ. Micr. Sci. vol. xvi. p. 377. 



