DEVELOPMENT AND LIFE-HISTORIES OF TELEOSTEAN FISHES. 689 
egos 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 flesus, 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 evaries, 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 Salmonidz, 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 G'astrosteus, 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 im 
considerable masses, or forms a thick, tenacious layer outside the zona radiata in eggs 
such as those of Perca fluviatilis, 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. + Vide No. 104, p. 363, &e. I Vide No. 106, p. 434. 
VOL, XXXV. PART ITI. (NO. 19) oT 
