382 



Part III. — Seventh Annual Report 



Fig. 4. Fungus growing on minnow, showing the successive formation 

 of sporangia, many of which are of a spherical form, 

 x 45 diameter. 



Fig. 5. Same as figs. 1 and 2, but more highly magnified, and showing 

 the oosporangium-like body. x 320 diameter. 



Fig. 6. Same fungus as figs. 1, 2, and 5, but showing the condition 

 assumed after thirty-six hours growth in water. Sporangia 

 are here seen, some having discharged their spores, and in the 

 centre a new sporangium may be seen growing up into the 

 case of a sporangium just emptied. x 80 diameter. 



Fig. 7. A ripe sporangium from same cultivation, more highly magnified, 

 x 1G0 diameter. 



XI. NOTE ON THE INTERCROSSING OF MEMBERS 

 OF THE GENUS SALMO. 



The complex and interesting subject of hybridism has received in 

 recent years a large amount of attention. It used to be generally held 

 that the production of fertile hybrids from the intercrossing of parents 

 specifically distinct could not occur, and that if fertile progeny resulted 

 from a cross between apparently distinct species it was in reality a proof 

 of specific identity. The supposed invariable sterility of hybrids was 

 looked upon as a provision to guard against the promiscuous intermingling 

 of species, and no point has been more insisted upon as a distinction 

 between species than the incapacity to produce mutually fertile offspring. 

 The further investigation has proceeded into the instances of hybridism, 

 and the more extended the observations made, the more it has been 

 rendered evident that this distinction of mutual sterility is not an invari- 

 able rule. It has been conclusively proved that hybrids are not invari- 

 ably sterile, but that their reproductive capacity may vary from complete 

 sterility to complete fertility. 



Among fishes there are two cases recorded of hybrids having been pro- 

 duced between species belonging to different families, namely, between 

 the brook trout and burbolt,* and between a female of the herring family 

 (Cliqwa or Alosa) and a male striped bass (Moccus lineatus) ; f but doubt 

 has subsequently been cast upon both these cases. The fact, however, 

 that fish belonging to different families may be mutually fertile has been 

 recently shown by some experiments of Sir Thomas Scott, one of the 

 naturalists of the Fishery Board for Scotland. In May last, on board the 

 'Garland,' he fertilised the ova of the common gurnard (Triyla gur- 

 nardus) belonging to the family Cottidai with the milt of the whiting 

 (Gachis merlangus) belonging to the family Gadidse.J Development went 

 on for 1J days, when the ova were found to have begun to sink, and 

 they subsequently died; apparently from the want of fresh sea- water, 

 when the vessel was lying over Sunday in harbour. Mr Scott in June 

 last also fertilised the ova of the lemon sole (Pleuroneetes mierocejjJialus) 

 with the milt of the turbot (Rhombus maximus), fish belonging to different 

 divisions of the Pleuronectida3.§ The eggs were unfortunately killed by 

 dust getting into the water 3J days after impregnation, but develop- 

 ment had been rapid, the embryo was well formed, and hatching would 

 probably have taken place on the seventh or eighth day. These experi- 



* Day, British and Irish Salmondire, p. 47. 



t Bull. U.S. Fish Commission, vol. ii. p. 187, 1882. 



X Nature, vol. xl. p. 163. § Nature, vol. xl. p. 253. 



