48 DR. J. MURIE ON IRREGULARITY [Jan. 13, 
the retardation or hastening of development. So, therefore, tempo- 
rary arrest of growth in Salmonoids is but an expression of the same 
law ; and it is worthy of special note that Salmon-ova preserved 
in ice are hatched later than when placed in a more suitable tem- 
perature. 
13. That the proportional growth of head to body &c. of Sal- 
monoids confined in fresh waters bears a diminished, though steady, 
ratio to that between Parr and adult Salmon. Thus it would seem 
that the same disposition as to the growth of parts is manifest, but 
antagonized or hampered by the unnatural conditions extant. 
14. That solid evidence is published of sexually mature male Sal- 
monParr being frequently met with in natural conditions. Experimen- 
tally, milt from such has impregnated Grilse-ova, the brood resulting 
showing diminution of early growth compared with Salmon-milt 
and ova, Grilse with Salmon, and Grilse with Grilse. It may be con- 
jectured, therefore, that the produce of the former parents would be 
much more likely to evince variation as regards development and 
migratory instinct than would fry derived from full-formed fish. 
15. That such legitimate though unequal unions should perad- 
venture happen, may very plausibly be assumed to be the case, 
rather than that hybridism between specifically different forms, 
spawning at separate dates, does often ensue. 
The above fifteen points, even when sifted and divested of extrane- 
ous remarks and unguarded assertions, still form a compendium 
which materially urges the following convictions :—(a) That though 
as a rule Salmon necessarily spend periods of their life in sea-water, 
circumstances may conduce to this being postponed temporarily or 
indefinitely. (j3) That a very appreciable arrest of growth is the 
consequence where retention to a limited area of water obtains. 
I leave it as an open question, whether S. salar may not vigorously 
grow aud multiply in extensive lakes and running streams, though, 
I may add, the preceding convictions prepare the mind for that 
belief. 
Respecting the term ‘arrest of development,” which my friend 
Mr. Buckland holds can only significantly be applied to a Sea-salmon, 
and in itself is not scientifie, I entirely disagree with him. I grant 
the phrase is one seldom if ever used by ichthyologists or in practical 
natural history ; but in pathological anatomy, and the kindred subject 
of malformations or teratology, it isof greatimport. The celebrated 
Russian embryologist Wolff suggested the term, and the no less 
famous comparative anatomist J. F. Meckel followed, and first used 
the expression ( Bildungshemmung) commonly adopted by succeeding 
writers on malformations—a sufficient guarantee for its scientific 
accuracy. 
The dwarf formation, abnormal diminutiveness, or retardation of 
growth that affects the Salmon in question is essentially due to 
a congenital or acquired arrest in the growth or development of the 
organs or system generally. Growth may be checked either in the 
embryo condition or subsequently to birth ; and the latter appears to 
be the case with the fish under immediate consideration. That is 
