MiY 1, 1895. 



KNOWLEDGE. 



99 



buried in closed cells, the eggs of the fish remain partly 

 exposed, and are thus carried about till they are hatched ; 

 the rugosities then disappear from the skin of the abdomen 

 of the parent, which resumes its normal smoothness. 



Abdomen of Aspredo hatrachus, witli the ova attaelied; at a, the ova 

 are removed, to show the spongy structure of the skin, and the 

 processes filling the interspaces between the ova. Natural size. 

 From Giinther's " Study of Fishes." 



Everybody who has been in the habit of partalsing of 

 whitebait will probably have occasionally observed among 

 the contents of his plate a long, slender, bony fish, with 

 a pipe-like nose, which has evidently no claim to kindred 

 with its neighbours. This fish is a young representative of 

 the pipe-fishes, which, together with the so-called sea- 

 horses, so well known for their habit of curling their tails 

 round the stems of seaweed, constitute a family especially 

 remarkable for the variety and curious nature of their 

 nursery arrangements. Among these an Oriental genus of 

 small pipe-fishes {Sulenostdinu) agrees with the fish last 

 mentioned in that the female takes charge of the eggs. 

 For this purpose she is provided on the lower surface of 

 her body with a roomy pouch, formed by the coalescence 

 of the pelvic fins with the skin of the abdomen. The 

 inner walls of this pouch are furnished with long filaments, 

 which aid in keeping the egg in position ; and it is highly 

 probable that after the young fish are hatched they are 

 retained for some time by attachment to the walls of the 



chamber. In the true pipe-fishes {Si/mjnnthm), on the 

 other hand, the task of looking after the nursery falls to 

 the males, which are provided with a long pouch on the 

 under surface of the tail, formed by a fold of skhi arising 

 on each side, and the two meeting in the middle line. 

 How the eggs are convej-ed into this pouch we are totally 

 unaware, but when once there, they are completely 

 enclosed by the junction of the edges of the two folds of 

 skin, and thus remain till they are hatched into minute 

 eel-like pipe-fish, which soon make their way into the 

 world by thrusting open the folds of the pouch. In the 

 sea-horses, the development is carried one stage further, 

 the nursing pouch being completely closed along the 

 middle line, and only communicating with the exterior 

 by means of a small aperture at the anterior end, 

 through which the eggs are by some means or other 

 introduced, and by which in due course the young make 

 their escape. Certain pipe-fishes {I >or[/ichtJii/s) diSev irom. 

 the ordinary forms in that the males have the pouch 

 situated beneath the abdomen instead of under the tail ; 

 and it is not a little remarkable that in certain allied 

 genera {Xfmphix, etc.j the eggs are simply attached to the 

 lower surface of the abdomen of the male without the 

 development of a pouch. We have thus an excellent 

 instance of the evolution of a special organ, so far as 

 the abdominal pouch is concerned ; but it would seem 

 highly probable that the caudal pouch of the allied forms 

 must have been independently evolved, in which event 

 we should have a remarkable example of parallelism in 

 development. 



Although many fishes retain their eggs within their 

 bodies until the young are hatched and attain a consider- 

 able size, we are not aware that any others have special 

 arrangements for carrying about their eggs after extrusion, 

 with the exception of the aberrant lung-fish {Protopterus) 

 of tropical Africa. In this genus 

 the numerous eggs and embryos 

 are reported to be nursed in a 

 long gelatinous pouch attached to 

 the sides of the back of one of 

 the parents, although which of 

 the two is charged with this 

 office does not appear to be ascer- 

 tained. Several kinds of fish are, 

 however, in the habit of con- 

 structing nests for the reception 

 of their eggs, while a few take 

 advantage of other animals for 

 their protection. For instance, the 

 females of the small roach- 

 like fishes, of which the Con- 

 tinental bitterling (Uhoileus 

 iiinarus) is the only European 

 example, have the oviduct 

 periodically prolonged into a 

 tube of considerable length, by 

 means of which the eggs are 

 introduced within the shells of 

 living freshwater bivalve molluscs, 

 where they remain secure from Sub-caudal poucli of •S'^h^'- 

 foes until hatched. Among the ««««»»"»■, with the young 



, , .,j. • ,, " 4. ready to leave the pouch, 



nest-buildmg species the most one'side of the membrane 



familiar are the bullheads ( Cottus), ^f the pouch is pushed aside 



sticklebacks (Gastrostcus), and to admit of a view of its 



lump-suckers (Cyclopterus), in interior. Natural sire. From 



all of which, as in the other Oimther's" Study of Fishes." 



instances, the nest is formed and guarded by the male 

 fish. In the sea-stickleback the nest is a large structure 

 composed of pendant seaweeds, tightly bound together into 



