The male is much like the female, but more slim, and the milt just like that of other fish. I can only conjecture that fecundation is accomplished through the medium of the sea-water, admitted by the curiously-contrived floodgate of the female, carrying in the milt-germs, and washing them over the ova.
The actual period of utero-gestation I am by no means sure about, but I am inclined to think they breed twice in the year. It is worthy of remark that the young mature fish are very large, when compared with the size of the mother. In a female fish eleven inches in length, the young were three inches long—the adult fish four-and-a-half inches high, the young an inch.
The only instance I can find recorded of a viviparous fish bearing any analogy to the Embiotocidæ is the viviparous blenny (Zoarces viviparus, Cuv.). Of course I exclude the sharks and rays. Of the viviparous blenny little or nothing appears to me to be known. On reference to Pennant’s ‘British Zoology,’ all he says is, that it was discovered by Schonevelde, and that Sir Robert Sibbald afterwards found it on the Scotch coast, and it was mentioned by Linnæus in his account of the Swedish Museum.
I quote the following paragraph verbatim from Pennant’s ‘British Zoology.’ Speaking of the blenny, he goes on to say: ‘It is viviparous, bringing forth two or three hundred young at a time. Its season of parturition is a little after the depth of winter; before midsummer it quits the bays and shores, and retires into the deep, where it is commonly taken. It comes into the mouth of the River Esk at Whitby, Yorkshire, where it is frequently taken from off the bridge.’
In Cuvier’s ‘Animal Kingdom’ (vol. i. ‘Fish’), all I can glean is that the blenny is viviparous. Yarrel, in his ‘British Fishes,’ speaks of a Mr. Low, who put a number of the small fishes (the young of the blenny) in a tumbler of sea-water, in which they increased in size, but eventually died from the want of fresh-water. Again, he quotes a Mr. Neil, who saw in the Edinburgh market, in 1807, several dozens of young fish escape alive from the female. ‘The arrangement of the perfectly-formed young in the fœtal sac of the gravid female is very remarkable.’
It is quite clear from the above quotations that there is an analogy, if not a close one, between the reproductive organs of the blenny and those of the viviparous fish from the North-west seas; for ‘the fœtal sac of the gravid female’ evidently means that there is a kind of placental sac, in which the young are contained; but it leaves us quite as much in the dark as ever as to how fœtal life is supported. As the ova deposited in the usual way (when fecundated) contains all that is requisite for the development of the embryo, it is just possible that the same process goes on in the womb of the female viviparous fish, and that the fœtal sac is only a wrapper, formed by the widened end of the ovary. But still I maintain that it fulfils a far more important duty.
I fear I have been rather prolix in the foregoing descriptions, but I must plead the novelty and importance of the subject as my excuse. The most beautiful of all the species of these fish is the sapphire perch (so called by the traders), very plentiful in Puget’s Sound. Eighteen exquisitely beautiful mazarine-blue lines or stripes mark its entire length from head to tail; and above and below this line are a number of spots of most dazzling blue, arranged in a crescent shape, about the eyes and gill-covers. Between these spots the colour changes, as it does in the dolphin, throwing off a kind of phosphorescent light of varying shades of gold, purple, and green—the back bright-blue but darker than the stripes; the belly white, marked by golden-yellow streaks.
But now for the most important feature in the history of these fish—that of bringing into the world their young alive, self-dependent, and self-supporting, as perfect in their minutest organisation as the parent-fish that gives them birth. The generative apparatus of the female fish when in a gravid state may be defined as a large bag or sac. Ramifying over its surface may be seen a most complicated and strangely beautiful vascular arrangement—a network of vessels, the use of which is clearly to convey the lifegiving fluid to the infant fish, and carry it back again, after having served its destined purpose, to be revivified for future use. The way this sac is, as it were, folded, and the different compartments made for the accommodation of the embryonic fish, is most singular, and very difficult to describe clearly.
The best illustration I can think of is an orange. You must imagine the orange divided into its regular number of little wedge-shaped pieces, and each piece to represent a fish; that the rind of the orange is a delicate membrane, having a globular shape, and easily compressed or folded. You now desire to fit the pieces together again in the original orange-shape, but you must begin on the outside of the globular membrane, pressing in with each section a fold of membrane (remember that each represents a fish); when each piece is in its place, you will still have the sac in its rounded form, but the rind or membrane has been folded in with the different pieces. If I have made myself understood, it will be seen that there must be a double fold of membrane between each portion of orange. This is exactly the way the fish are packed in this novel placental sac. If it were practicable to remove each fish from its space, and the sac retain its normal shape, there would be twelve or fourteen openings (depending upon the number of young fish), the wall of each division being a double fold of membrane—the double edges wrapping or, as it were, folding over the fish. Now make a hole in the end of this folded bag, and blow it full of air, and you get at once the globe-shaped membranous sac I have likened to an orange.
The fish are always arranged to economise space: when the head of a young fish points to the head of its mother, the next to it is reversed, and looks towards the tail. I am quite convinced that the young fish are packed away by doubling or folding the sac in the way I have endeavoured to describe. I have again and again dissected out this ovarian bag, filled with fish in various stages of development, and floating it in saltwater, have, with a fine-pointed needle, opened the edges of the double membranous divisions that enwrap the fish—(the amount of overlapping is of course greater when the fish is in its earlier stages of development). On separating the edges of the sac, out the little fishes pop. I have obtained them in all stages of their growth,—but sometimes (and this not once or twice, but often) have set free the young fish from its dead mother. Thus prematurely cut loose from its membranous prison, the infant captive, revelling in its newly-acquired liberty, swam about in the saltwater, active, brisk, and jolly, in every particular, as well able to take care and provide for itself as its parent. The female external genital opening is situated a little posterior to the anal opening; the orifice is at the apex, and in the centre of a fleshy conical protuberance, which is in fact, a powerful sphincter muscle, moored, as it were, in its place by two strong muscular ropes, acting from and attached to the walls of the abdomen.