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Show -48 DR. J. MURIE ON IRREGULARITY [Jan. 13, the retardation or hastening of development. So, therefore, temporary 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 temperature. 13. That the proportional growth of head to body &c. of Salmonoids 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. Experimentally, 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 conjectured, 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 extraneous 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. (/3) 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 and 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 m y friend Mr. Buckland holds can only significantly be applied to a Sea-salmon, and in itself is not scientific, 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 is of great import. 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 |
