April 1 6, 1885] 



NA TURE 



555 



ing member of the Institute of Fiance. There seems 

 little need to enumerate all the honours that were con- 

 ferred on him during the half century that he was known 

 as one of the distinguished zoologists of Europe. 



In the important and indispensable catalogue of Scien- 

 tific Papers published by the Royal Society, we find a 

 list of over 130 memoirs ascribed to Prof. Von Siebold. 



Failing health during the last few years interrupted this, 

 up to 1S74, steady flow, and Dr. Ehlers undertook much 

 of the labour of editing the Zeitschrift. Those who had 

 a personal knowledge of Von Siebold will remember his 

 pleasant and friendly manners, the readiness with which 

 he placed at the students' disposal all the information in 

 his power, and the visitor to the Zoological Museum at 

 Munich will not soon forget the vast stores, not only 

 collected, but scientifically arranged under the super- 

 intendence of Von Siebold. 



THE EGGS OF FISHES 1 

 II. 



THE condition of the fish-fauna of the various grounds 

 may be estimated to some extent by the number of 

 the floating ova near the surface. We have seen that Sars 

 found the water crowded with the multitude of ova off 

 the Loffoden Islands, where enormous numbers of cod 

 are captured. In our seas no fishing-bank is so prolific, 

 the greatest number of ova occurring on Smith Bank, off 

 Caithness, and the next on the rich grounds off the Island 

 of May -both of which present a great contrast with the 

 meagre supply of eggs of round fishes floating in our own 

 bay. The proportional numbers in each case accord very 

 well with the captures of adult cod in the several areas. 



lit can be more interesting to the naturalist than 

 the surface of the sea, in the condition just mentioned, 

 about the beginning of April. The rough water of the 

 great fishing grounds — such as off Smith Bank, and 

 somewhat further from land — is enlivened by large groups 

 of gulls, guillemots, and the ubiquitous gannets, ap- 

 parently feeding on the smaller fishes which have been 

 attracted to the surface by the wealth of food. At short 

 intervals the long dorsal fin of a large killer appears 

 above the surface, and the water behind it is churned into 

 foam by the powerful strokes of its tail ; while a small 

 group of bottle-noses (another kind of toothed whale) is 

 recognised by the noise and foam, as one or more leap 

 from the sides of a huge wave. The tow-net collects 

 large quantities of ova and minute fishes which have just 

 escaped from the egg. It further shows that innumerable 

 minute crustaceans, such as Copepods (e.g. Calanus fin- 

 / , Gun., arid Temora longicornis, O.F.M.), multi- 

 tudes of the young, or nauplius-stage, of sea-acorns, 

 , and peculiar Annelids Uoida) are present. It is 

 evident, therefore, that the young fishes are placed in the 

 midst of a rich surface-fauna, the more minute forms of 

 which would readily serve as food. 



In the foregoing remarks on the floating eggs of British 

 food fishes, those of the cod, haddock, and whiting, have 

 been chiefly alluded to. We shall now refer to others, 

 either wholly or partially unknown till this year. I have 

 already mentioned that Sars found certain floating eggs 

 mingled with the former on the surface of the sea, and 

 identified the young, after hatching, as gurnards. In the 

 present case the eggs were removed from the adult gur- 

 nard, and hatched at St. Andrew's in about a week, so 

 that a further step has been made. The eggs of the 

 gurnard float as buoyantly as those of the cod and 

 haddock, but they are considerably larger. Each has a 

 very distinct oil-globule opposite the germinal area, which 

 generally is directed downwards. Some are of opinion 



1 Introductory Lecture delivered to the Class of Natural History in the 

 : of St. Andrews, on November 10, by Prof. Mcintosh, LL.D., 



r'.R.S. Continued from p. 536. 



that the floating of the eggs of such fishes as we are now 

 considering is due to the oil-globules, but the eggs of 

 several fishes, e.g. those of the salmon, have a larger 

 quantity of oil, and yet they do not float. The specific 

 gravity of the eggs is slightly less than that of the sea- 

 water ; but the precise connection between the floating of 

 the living ova and the sinking of the dead has yet to be 

 made out. Such would form, indeed, a most valuable 

 and interesting subject for investigation at the Marine 

 Laboratory. So easy is it to hatch the eggs of the gurnard 

 that the water in the instance just narrated was not 

 changed. The rapidity with which the development of 

 the embryo goes on in the egg is remarkable, for in 7 

 or 8 days the young are extruded, whereas in the 

 salmon, for instance, no less than 60 days are required 

 even in a room with a temperature much higher than that 

 of the open air. If the eggs of the salmon are permitted 

 to hatch in an ordinary river, a period of from 95 to 

 120 days is usually necessary for hatching. The very 

 great difference, therefore, between the marine and fresh- 

 water fishes in this respect is apparent. 



The only flat fish in which the ova had been found to 

 float was the plaice, which Dr. Malm had examined in the 

 Baltic. In May of this year, however, the eggs of the 

 common flounder in St. Andrew's Bay showed tire same 

 feature. They floated buoyantly on the surface of the 

 water. Prof. Huxley at this time having suggested that 

 perhaps the floating or sinking of the ova was a question 

 of temperature, the eggs of this species were used in 

 some experiments. They had been removed from the 

 fish on May 2, and placed in the Marine Laboratory. 

 On the 5th the majority still remained on the surface, 

 those on the bottom having been carried down by the 

 attachment of sand-grains. A number from the surface 

 were placed in a test-tube. After standing an hour the 

 majority were floating on the surface, one or two lay on 

 the bottom, while others rested in mid-water. Placed in 

 a vessel of water at 98", the eggs exhibited lively move- 

 ments for several minutes, being carried up and down by 

 the currents, but never remaining at the bottom. The 

 test-tube felt quite warm to the touch, yet the eggs floated, 

 and remained floating, as buoyantly in the warm water as 

 in the cold, so that their floating in the sea is not a question 

 of temperature. 



An interesting sequel, further, remains to be told in 

 connection with this experiment, in which the test-tube 

 had been placed aside and forgotten. On May 10, while 

 explaining the matter to Prof. Ewart, he noticed motion 

 in the test-tube, and I found that the eggs which had been 

 raised to a temperature of 98 ' had given birth to little 

 flukes, which thus survived the exigencies of their sur- 

 roundings, both as regards temperature and water. These 

 little creatures are as symmetrical in outline as the young 

 cod or haddock, an eye being placed on each side of the 

 head, while in the adult flounder, as you are all aware, 

 both eyes are on one side (the right or coloured one). 

 The pigment is quite different from that of the young 

 cod, being of a peculiar pale olive or brownish yellow by 

 transmitted light, and the cells seem to be less branched. 

 Their motions also diverge from those of the cod, for 

 the little creatures hang head downwards in the water, 

 cither perpendicularly or obliquely, the yolk-sac being on 

 the upper line of the slope. They then move upward, 

 hang as formerly, or slowly descend, repeating these 

 motions frequently. The young cod, on the other hand, 

 dart nimbly about near the surface of the water, and bear 

 themselves quite differently. 



But to return to the ova. Before the summer that has 

 just passed, it was not known whether the ova of the 

 turbot, sole, and lemon-dab — all important and valuable 

 food fishes — floated or sank. Accordingly such fishes 

 were a source of special interest. It was not till the end 

 of June and in July that perfectly ripe turbot could be 

 procured, and then the small ova were found to float as 



