242 



HARDWICKE'S SCIENCE- GOSSIP. 



[Nov. 1, 1S60. 



Fig. 227- The Viviparous Fish (Ditrema argenleum). 



down the side (the plan I usually adopt to skin a 

 fish), to my intense surprise out tumbled a lot of 

 little fish ! My wildest dreams had never led me to 

 suppose a fish I then thought a bream, or one of the 

 perch family, could be viviparous. I at once — 

 perhaps hastily — arrived at the conclusion that the 

 greedy gourmand had eaten them. Dropping my 

 knife, I sat in a most bewildered state, looking at 

 the fish. 



I soon observed that each little fish was a fac- 

 simile of the larger, and in shape, size, and colour, 

 were exactly alike. Erom the position, too, they 

 occupied in the abdomen of the larger fish I was led 

 at once to see the error of my first assumption 

 that they had been swallowed. Carefully dissecting 

 back the walls of the abdomen, I discovered a 

 delicate membranous bag or sac, having an attach- 

 ment to the upper or dorsal region, and doubled 

 upon itself into numerous folds or plaits, and be- 

 tween each of these folds was neatly packed away a 

 little fish. The bag was of a bluish-white colour, 

 and contained fourteen fish. I had no longer any 

 doubt that the fish was viviparous. 



Now we come to a ticklish question : How arc 

 the young fish vitalized in the abdomen of the 

 mother ? I believe the ova, after fertilization, in 

 the first place undergoes the same transformation in 

 the ovarium as it would do supposing it to have been 

 spawned and fecundated in the ordinary spawning- 

 bed— but only up to a certain point ; then, I think, 

 the membrane enfolding the eggs, which have by this 

 time assumed a fish-like type, takes on, in some 



degree, the functions of a placental membrane, and 

 the young fish are nurtured much in the same way 

 as in a mammal. 



But a third change takes place. There can be no 

 doubt that the young fish I cut out, and which swam 

 away, had breathed before they were freed from the 

 mother ; hence I am led to infer that a short time 

 prior to the birth of the young, sea-water has access 

 to the sac, washes over the infant fishes, thus en- 

 abling the gills to assume their normal action, and 

 by-and-by the little fellows are launched into the 

 deep, therein to shift for themselves. There are 

 strong transverse muscles, which act from the 

 abdominal walls, these, I imagine, are in some 

 way concerned in admitting the sea-water. How 

 impregnation takes place I at once confess I do not 

 know. The male is much like the female, but more 

 slim, and the milt just like to that of other fish. 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 11 inches long, the young 

 were 3 inches long; the adult fish 4| inches high, 

 the young 1 inch. 



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-support- 

 ing, as perfect in their minutest organization as the 

 parent fish that gives them birth. The generative 

 apparatus of the female fish, when in a gravid state, 

 may be definectVs a large bag, or sac, over the surface 

 of which a most complicated and strangely-beau- 

 tiful network of vessels spreads in every direction. 



