SALMONID^E. 83 



(January 8th, 1881), that they become, as he found them, big-headed, lank, and 

 black looking. But there may be a reason for this, as insufficiency or inappro- 

 priateness of the food in their new home, which precludes their thriving or even 

 continuing in health. Should, on the contrary, the place prove appropriate, they 

 may thrive even though they are unable to return to the sea. McCulloch 

 (Journ. Roy. Inst., no. xxxiv, p. 211) has stated that the salmon-trout is now a 

 permanent resident in a fresh water lake in the island of Lismore, one of the 

 Hebrides, and without the power of leaving it or reaching the sea. There it has 

 been known for a long course of years, perfectly reconciled to its prison, and 

 propagating without any apparent difficulty. Eggs of the sea-trout havino- been 

 transmitted to Tasmania, some of the young retained in a fresh water pond (see 

 pages 84, 86) have bred showing no symptoms of sterility. This breeding has 

 taken place each successive year since, and the fertility of the ova seems to be 

 exceptional, for every one of the 142 ova sent to the Otago Acclimatization 

 Society produced a fish. 



It is evident that our anadromous sea-trout may take on a fresh water state of 

 existence, and breed there ; irrespective of which by imperceptible changes we 

 find it in every country passing from one form into the other, as I shall give 

 instances when treating of the different varieties. This, of course, raises the 

 question of which form Salmo orcadensis, 8. estuarius, &c, most resemble, the 

 anadromous 8. trutta or the fresh water 8. fario. Admitting the two latter as 

 being merely the extreme limits of one species, it becomes unnecessary to decide 

 whether the diminution in the number of the vomerine teeth* is symptomatic 

 of the fresh water form developing towards its larger relative the anadromous 

 sea trout, or whether it is the sea trout retrograding towards its parr dentition, or 

 that which is persistent in the Salmo fario. Colours, it is true, are not very 

 reliable, but these forms more nearly approach the fresh water than the saline 

 varieties, a change which appears invariably to occur sooner or later in 

 anadromous forms which become permanent residents in fresh water. 



But although the foregoing tends to prove that anadromous forms may pass 

 into fresh water non-migratory species, further proofs are necessary that it does 

 so in this particular instance. The distinction between the two races being 

 seen first in the comparatively more complete system of dentition in the fresh 

 water forms, their generally longer heads and decreased number of ccecal 

 appendages. The dentition varies excessively ; thus we find examples possessing 

 the colours, form, &c, of the brook-trout resident in brackish waters or even 

 the sea, but mostly not invariably possessing the limited number of vomerine teeth 

 of the anadromous form. On the other hand we find anadromous forms (in colour) 

 passing into fresh water, and the teeth assuming that present in the brook-trout 

 or retaining their parr dentition. I am unable to see in this, as has been 

 suggested, hybridization, or more properly speaking, a " graduated hybridiza- 

 tion," for every gi-adation can be seen, the links in the chain are perfectly complete, 

 as may be perceived at the British Museum, in the Welsh series of 8. cdmbricus, 

 or in the 8. trutta of the Tweed. On the other hand, in the same institution 

 are so called hybrids between the 8. gallivensis, Giinther, and the brook-trout. 

 The comparative length of the head is likewise subject to variation, there being 

 both the long-headed and short-headed races of the more south and west sewin, 

 and also of the sea trout on the east coast of Britain. And, lastly, as regards the 

 number of ccecal appendages asserted as a character which may materially aid 

 in discriminating a species. I have already (p. 56) given reasons for declining 

 to accept this in respect to our fresh water trout, and will now adduce further 

 ones to show that neither is it reliable in the sea forms. A very instructive 

 instance is to be found in the case of the ova of sea-trout, which were transmitted 

 to Tasmania, and one of the adult progeny of which, 18 inches in length, was 



* Whether the vomerine teeth are at once replaced when lost, or at certain periods shed, is a 

 question admitting of doubt. Mr. Harvie Brown has pei-sonally observed that the lingual teeth are 

 shed in June, July, and August in the brook-trout, new ones mostly taking their place, loose in their 

 sockets at first and not filling the cavities made by the old cast-oft - ones. Should this be invariable 

 it shows that the size of the lingual teeth is no criterion as to species. 



6 * 



