130 



NATURE 



[yuKe 6, 1889 



-such lamentable teaching failures. Under these circum- 

 stances it would be ridiculous to " trust the teacher, trust 

 him to teach, trust him to examine;" for, bad as 

 examiners are, teachers are worse — partly for the same 

 reason as that for which white sheep eat more than black, 

 viz. that there are more of them. 



And is it not also vain to attempt to replace the 



^Exaimination system, even at the Universities, by a system 



*af Thesis writing on some particular subject selected by 



Hne candidate, the Thesis being written by him at home, 



with ample opportunity for composing it out of works of 



reference, or with the assistance of his friends, with the 



addition of a small make-believe of "original research ?" 



We are told by one of the writers in the Nineteenth 



Century that, under our Examination system, England is 



losing her intellectual giants, men who are a head and 



shoulders above their contemporaries ; but I ask is the 



writer aware that we have still among us Sir William 



Thomson, and that we have only recently lost Clerk 



Maxwell ? People who speak thus seem to think that we 



are to expect a crop of intellectual giants to sprout up 



like a crop of mushrooms, and to be ready whenever we 



want them. 



I would say in conclusion — let us retain Examinations, 

 make them tests of a knowledge of the applications of 

 principles, so that they will be real tests of intelligence, 

 and not of cram ; do not make them so difficult and so 

 high-flown as they often are ; and, finally, do not encourage 

 the hurrying and skimming through a large number of 

 different subjects, but make sure of the foundations by a 

 more thorough and leisurely system of study. 



THE LIFE-HISTORY OF A MARINE 

 J'LOD-FISH} 



I. 



T T is but a few years since the life-history of our most 

 -*■ important marine food-fishes was involved in con- 

 siderable obscurity — not only as regards popular views, 

 but even in respect to the knowledge of men of science. 

 Thus, for instance, in the years 1883 and 1884 the almost 

 unanimous opinion of British fishermen was that our 

 common food- fishes sought the shallow water of the bays 

 and inshore ground generally for the purpose of depositing 

 their eggs on the bottom. No observations specially 

 bearing on this point had been made by British zoologists, 

 and a series had to be undertaken for a public inquiry 

 then in progress — with a result which demonstrated how 

 extensive the reverse of the popular notion was. Again, 

 certain comparatively recent authors on British fishes 

 speak of a common fish like the gurnard as spawning 

 twice a year, whereas, after careful observation, no evidence 

 in support of this view has been obtained. The same 

 obscurity veiled the larval and post-larval conditions of 

 most of the food-fishes, even G. O. Sars — in regard to the 

 latter stage — describing no intermediate forms between 

 the larva of 6 mm. and the post-larval stage of 24 mm. in 

 the cod, almost the only fish to which some attention 

 had been paid. 



On the other hand, our knowledge of the development 

 and life-history of the fresh-water fishes — such as the 

 salmon, trout, and charr — has for many years been well 

 understood — thanks to the labours of Louis Agassiz and 

 Vogt in Switzerland, Coste and Lereboullet in France, 

 Ransom in England, and Shaw in Scotland, on the 

 scientific side, and of the noblemen and gentlemen of 

 Perthshire (ably seconded by Robert Buist) in connection 

 with Stormont Field Ponds on the Tay, on the popular 

 side. Much information has also been recently obtained 

 by Dr. Day and Sir J. Gibson Maitland at the excellent 

 ponds of the latter at Howietoun. 



' A Discourse deliverea by Prof. W. C. Mcintosh, F.R.S , at the Royal 

 lii5titution, on Friday, February i, 1889. 



A short time ago, relying on experience derived from 

 fresh-water fishes, not a few imagined the eggs of marine 

 fishes as readily visible and tangible objects — possibly 

 associated in their minds with certain practices in trout- 

 fishing, or it may be with the manufacture of caviare. 

 Recent investigations, however, have shown that in most 

 marine food-fishes the eggs are minute glassy spheres 

 which float freely in the ocean. For a knowledge of this 

 fact we are indebted in the first instance to Prof. G. O. 

 Sars, of Christiania, a naturalist trained from boyhood 

 under a distinguished father, and who, by a fortunate 

 appointment to a fishery post in Norway, was enabled to 

 discover that the eggs of the cod, haddock, and gurnard, 

 floated in the water, or, as we term it, were pelagic. He 

 thus opened up a new field in the economy of the food- 

 fishes, which in a great maritime country like ours ought 

 not to have remained so long unexplored. 



Lately, however, attention has been earnestly directed 

 to the subject, and the labours of Cunningham, Brook, 

 Prince, and others have made considerable advances in 

 this department. 



It is now known that the great majority of our British 

 marine food-fishes — indeed, all our most valuable kinds 

 (including even the sprat and the pilchard amongst the 

 Clupeoids) produce minute eggs — as transparent as crystal, 

 and which float freely throughout the water. These eggs, 

 moreover, are not all shed at once, as in the case of the 



Fig. I.' — Pelajlc egg of the ling (enlarged). 



salmon, but successive portions of the ovary become ripe, 

 and the eggs then issue externally. If by any accident 

 or irregularity — as for instance the confinement of a 

 flounder in an unhealthy tank — this gradational issue is 

 interfered with, the animal dies from the great distention 

 of the body caused by the pent-up eggs. In the case of 

 the cod this gradual issue of the eggs continues probably 

 for a week or two, so that the progeny of a single fish in 

 one season may vary considerably in size. 



From the early months of the year onward to late autumn 

 the sea off our shores thus abounds with pelagic eggs, 

 those of the rockling, haddock, and sprat being amongst 

 the earlier forms, while the later include those of the sole. 

 As indicated in the Trawling Report, and now supported 

 by further experience, it would be a very difficult matter 

 indeed to arrange for a close time in the sea — that is to 

 say, for a limited period during which the mature fishes 

 might be permitted to spawn in peace. This, however, in 

 the case of individual species, such as the cod, might more 

 readily be,carried out, so as to save the mature fishes at 

 the spawning period. 



In a vessel of still sea-water these transparent glassy 

 spheres rise at once on issuing from the fish, and form a 

 stratum on the surface. Even the ripe portions of ovaries 

 removed from the rejected viscera on a pier will show the 

 same features, and thus, indeed, they first came before 

 the lamented Lord Dalhousie at Anslruther. In the sea, 

 however, they are seldom met with on the surface, and the 

 tow-nets require to be sunk a fathom or two for their cap- 

 ture, their specific gravity being so little less than that of 

 sea-water that they are carried hither and thither by the 



"^ I am indebt-d to Mr. E. E. Prince, B.A., for kindly aiding me with 

 sket:hes for the v • o Icuts. The sketch oi Moiella is by Dr. Scharff. 



