326 



A HISTORY OF FISHES 



yolk-sac are abundantly supplied with blood-vessels, and special 

 folds or processes of these walls become adherent to or penetrate 

 into the walls of the uterus, which are similarly highly vascular, 

 and through the conjoined vessels the blood of the mother 

 passes to her offspring. Even after birth young Sharks may 

 carry, for some time, the pendent yolk-sac, and continue to 

 derive some nourishment from that source (Fig. 117A, III). 



The actual extrusion of the young in Sharks and Rays has 

 rarely been observed, so that the observations made by Mr. 



rig. 117. DE\^LOPMENT OF SHARK AND BONY FISH. 



A. Three stages in the development of the Spiny Dog-fish (Squalus acanthias). 

 I and II — nat. size; III — X about \. (I. After Balfour) ; b. Three stages in the 

 development of the Salmon (Salmo salar). I and II — Alevins, nat. size ; III — 



Parr, X I. 



Coles on the birth of a Devil-fish {Manta) off the coast of Florida 

 are of particular interest. "Almost immediately after being 

 struck by the harpoon," he writes, "the Manta made the 

 sideways revolution alongside the boat, and just before the 

 tail had reached the perpendicular an embryo was violently 

 ejected to a distance of about four feet. The embryo appeared 

 tail first, folded in cylindrical form, but it instantly unfolded, 

 and its pectorals, moving in bird manner, retarded its descent 

 until the mother fish had disappeared below the surface. I was 

 almost in the act of securing this embryo when it was swept 



