DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 689 



eggs run out with little or no pressure, and the ovaries may often be thus emptied in a 

 few moments. Now if the ovaries of a female Cyclopterus lumpus, exemplifying rapid 

 deposition, be examined, we find, when in a ripe condition, that the contained ova 

 apparently become mature simultaneously.* In such a case great distension of the 

 abdomen occurs, and the eggs are deposited in a single large mass in a very short time. 

 In a female Cottus scorpius under observation, and likewise distended with ripe ova, 

 oviposition occupied only a few seconds. 



A very different condition obtains in other forms, such as Molva vulgaris or Pleuro- 

 nectes Jlesus, in which a large proportion of the ova ripen together, yet the act of extrusion 

 is more deliberate and slow; while in Gadus morrhua, or more distinctly in Trigla gur- 

 nardus, the eggs reach maturity by successive strata, a comparatively small proportion of 

 them being ripe and translucent. The latter generally pass posteriorly, and collect near 

 the genital opening — ready for extrusion, t Isolated ripe ova, however, are scattered 

 throughout the ovaries, and in such forms the extrusion of all the eggs in a single female 

 must extend over a prolonged period. 



While the ova remain in the body of the fish they are bathed in a mucilaginous fluid, 

 so that they easily glide over each other, and thus their egress is facilitated. This ovarian 

 mucus seems to have different properties in different species of Teleosteans, either dis- 

 appearing on mixing with water, as we see especially in the non-adhesive floating eggs of 

 the cod, haddock, whiting, ling, gurnard, skulpin, flat-fishes, and also in the demersal eggs 

 of the Salmonidse, or remaining glutinous and adhesive for some hours — the eggs clinging 

 strongly together and forming irregular spongy masses, as in British Cottoids, Discoboli, 

 various species of Gastrosteus, as well as the recently discovered ova of Anarrhichas. In 

 Lepadogaster,\ however, the ova are fixed singly to shells, sticks, sea-weeds, and other 

 structures. 



After submergence in sea water such ova become so strongly cemented that some 

 force is required to separate them, and the egg-masses of forms like Cyclopterus adhere so 

 firmly that many of the ova are usually injured in dislodging them. Whether the 

 mucilaginous nexus which binds ova like those of Lophius piscatorius together in 

 considerable masses, or forms a thick, tenacious layer outside the zona radiata in eggs 

 such as those of Perca Jluviatilis, be really an excessive secretion of the mucus spoken of 

 above or not is undetermined. 



Demersal ova appear to be deposited by the female on the very sites where the whole 

 course of development, up to the time of hatching, will be undergone. With pelagic ova 

 the case is very different ; during development they may wander far from the place of 

 deposition. 



It must be noted, however, in the case of the cod, and other food-fishes, that the 

 grounds upon which the adults congregate are those where the surface specially abounds 

 with their pelagic ova, as Sars first noted at Lofoten. 



Upon extrusion the buoyancy of pelagic ova is strikingly shown, for, if ripe, they at 



* Vide Nature, June 1886. t Vide No. 104, p. 363, &c. J Vide No. 106, p. 434. 



VOL. XXXV. PART III. (NO. 19). 5 T 



