552 MR SHAW'S EXPERIMENTAL OBSERVATIONS ON THE 



atmosphere 39°. On its first exclusion, the Uttle fish has a very singular appear- 

 ance. The head is large in proportion to the body, which is exceedingly small, 

 and measures about Jive-eighths of an inch in length, of a pale blue or peach-blos- 

 som colour. But the most singular part of the fish is the conical bag-like 

 appendage which adheres by its base to the abdomen. This bag is about two- 

 eighths of an inch in length, of a beautiful transparent red, very much re- 

 sembling a light red currant, and in consequence of its colour, may be seen 

 at the bottom of the water when the fish itself can with difl&culty be per- 

 ceived. The body also presents another singular appearance, namely, a fin 

 or fringe, resembling that of the tail of the tadpole, which runs from the dorsal 

 and anal fins to the termination of the tail, and is slightly indented. This 

 little fish does not leave the gravel immediatel}^ after its exclusion from the egg, 

 but remains for several weeks beneath it with the bag attached, and containing a 

 supply of nourishment, on the same principle, no doubt, as the umbilical vessel is 

 known to nourish other embryo animals. By the end of fifty days, or the 30th. 

 May, the bag contracted and disappeared. The fin or tadpole-like fringe also dis- 

 appeared by dividing itself into the dorsal, adipose, and anal fins, all of which 

 then became perfectly developed. The little transverse bars, which for a period 

 of two years (as I have already shewn) characterize it as the parr, also made their 

 appearance. Thus, from the 10th January till the end of IMay, a period of up- 

 wards of 140 days was required to perfect this little fish, which even then mea- 

 sured little more than one inch in length, and corresponded in all respects with 

 those on which I had formerly experimented, as well as with such as existed at. 

 that same time in great numbers in the natural streams. 



Although I was myself satisfied by the preceding facts that parr and salmon 

 fry were thus identical in kind, and differed only in respect to age, I was informed 

 that my inferences were objected to, in as far as there was not sufficient evidence 

 that the spawn experimented on was actually that of salmon, seeing that the- 

 same streams were accessible to other species of the genus. I therefore felt it in- 

 cumbent on me to supply this desu'ed link in the chain of evidence, and I accord- 

 ingly repeated ray experiments on ova which I saiv excluded, which, in fact, I 

 forced the salmon to exclude, in the manner after mentioned, preserving at the 

 same time the skins of the parent fish, for the satisfaction of the curious or 

 sceptical. 



Before proceeding to make additional experiments, it was necessary to lay 

 my experimental basins dry, not only for the purpose of removing the young 

 salmon of the preceding season's produce, but also to enable me to fit them up on 

 such a principle as would exclude any possibility of confusion either from the 

 overflowing of the ponds themselves, or from the flooding of the river Nith, on 

 the banks of which they are situate. The plan on which these ponds are con- 

 structed is shewn on Plate XXI. Every precaution was used not only to exclude 



