DKVKLOPAIENT OF FISHES. 295 



the period of ' fecundation ' approaches, the female osseous fish seeks 

 a favourable situation for depositing her spawn, usually in shoal 

 water, where it can be most influenced by solar warmth and light. 

 TJie marine Herring, Mackerel, and Pilchard approach the shore in 

 shoals : the fluviatile Salmon quits the estuary to ascend the river, 

 overcoming, with astonishing perseverance and force, the rapids or 

 other mechanical diificulties that impede its migration to the shallow 

 sources, whither the sexual instinct impels it as the fit place for ovi 

 position. The female fish is closely pursued by the male, sometimes 

 by two ; in the Capelin {MaUotus), these swim on each side of her, 

 aiding by their pressure in tlie expulsion of the spawn, and at the same 

 time impregnating it by diff*using over it the fluid of the milt : thus 

 absorbed in the sexual passion, they have been seen, on the shores 

 of Newfoundland, to rush on land in their spasmodic course over the 

 shallows, which they strew with the fecundated ova. In some 

 genera violent combats take place between the males. Mr. Shaw*, 

 a most able observer of the development of the Salmon, states : — 

 " On the 10th of January, 1836, I observed a female salmon of 

 about 161bs., and two males of at least 251bs., engaged in depositing 

 their spawn. The two males kept up an incessant conflict during 

 the whole day for possession of the female, and, in the course 

 of their struggles, frequently drove each other almost ashore, and 

 were repeatedly on the surface displaying their dorsal fins, and lash- 

 ing the water with their tails." " The female throws herself at inter- 

 vals of a few minutes upon her side ; and while in that position, by 

 the rapid action of her tail, she digs a receptacle for her ova, a portion 

 of which she deposits, and again turning upon her side she covers it 

 up by the renewed action of the tail ; thus alternately digging, de- 

 positing, and covering the ova, until the process is completed by the 

 laying of the whole mass, an operation which generally occupies thi'ee 

 or four days." 



In the ovo-viviparous osseous fishes, the well-developed clo- 

 acal papilla, in which the sperm-ducts terminate, doubtless serves 

 to ensure intromission. The superadded claspers in tlie male Phi- 

 giostomes lend more effectual aid in the act of internal impregnation ; 

 for in those species that are oviparous the ova are impregnated and 

 covered by a nidamental coat or ' shell ' prior to exclusion. 



Fcetation The observation of the more simple mode of impregna- 

 tion in osseous fishes, so analogous to that of the diojcious palms in 

 which the fertilising pollen is wafted through the aerial ocean and 

 strewed over the humid papillose stigmata of the female flower, 

 naturally suggested the idea of artificial impregnation, of wliich 



* CXXII. 



u 4 



