1870.] IN THE GROWTH OF SALMON. 43 
“The term arrest of development of the Smolt, Mr. Buckland 
thinks, is not a scientific term. Nature has ordained that the fish 
should not grow more than a certain size in fresh water; that is to 
say, there is a maximum of growth and size in the Smolt. The 
transmutation of the Smolt into a Salmon takes place in the sea. 
Here, for the first time, we find that wonderful provision (which 
Mr. Buckland lays great stress on), the storing of fat on the pyloric 
appendages. Smolts have no fat on the pyloric appendages; but 
Grilse have. Non-migratory Salmonidee have no pyloric fat; but 
Sea-trout possess it. 
“The reason why Smolts will never become Salmon in fresh 
water has some relation to this development into the superior 
from the inferior stage of organization. This stage is not necessary 
for life. Salmon will live a long time in fresh water in the inferior 
condition, yet never pass over the line of demarcation between the 
two stages, unless conditions for the perfection of the secondary form 
be present. This is shown in the fact that nature actually orders 
a new coat for the creature when it passes from the one condition of 
things to the other. 
“If the migratory instinct is impeded by human intervention, 
the dress assumed at such times disappears, and the fish (by a happy 
provision of Providence) continues to wear its Parr-coat, which, as 
the fish gets bigger, becomes increased in intensity. The ‘Heppers’ 
already spoken of exemplify this. 
“The arrest of development is a term, therefore, which can 
only strictly be applied to Salmon in the sea, inasmuch as the 
arrest is simply the first natural stage of the progressive series of 
growths. Such stages of Salmon-growth have a parallel in the 
changes of insect-form: thus egg =ovum, caterpillar =parr, chry- 
salis =Smolt, and the butterfly =Salmon, may be said to be the 
analogous stages whereby insect and Salmon pass from the imperfect 
to the perfect condition.” 
Among what I have classed as addenda comes, as undernoted, a 
Table of dimensions (B). In the first notice (P. Z. S. 1868, p. 253) 
I was only able to give in detail those of specimen No. 1; but 
No. 2 has died since, and thus permitted its linear measurements 
to be taken. I have placed alongside these five other specimens, 
four of which are nearly similar in length, and the other that of a 
full-grown fish. These are specimens described individually by Dr. 
Giinther in his Catalogue, and have been chosen by me to illustrate 
the proportional sizes and relations of the parts of the body to each 
other in an immature Salmon, a Sewin, a quasi-hybrid, a 8. nigri- 
pinnis, and a fully developed 8. salar. As the fractions used in 
the Catalogue are chiefly given in fourths, eighths, and sixteenths of 
an inch, I have converted these into decimals, enabling comparison 
between my two specimens and them more readily to be drawn 
therefrom. 
Columns I. and II. relate to the Society’s specimens, described in 
the previous paper. 
Column III. relates to a young male Salmon (Parr), from the 
