RAPPORTS. XIV: EHRENBAUM — 8 — 



to the bottom, the fish begin slowly to feed ; at first there are only a few, later on (e. g. in 

 March) about one-third of the trawl-caught mackerel are found with more or less con- 

 siderable contents in their stomachs. This I was able to discover from material landed 

 at the Hamburg market, and it has been demonstrated in a similar way by the Irish 

 investigators. 



The supposed blindness ot the mackerel arose from the fact, that the so-called 

 adipose lid, a translucent gelatinous scaleformed matter, which fills the orbit round the 

 eyeball, and which is perfectly clear in the living fish, turns opaque some time after 

 death, so that the appearance of blindness is given to a certain degree; this gelatinous 

 mass, however, though covering the greater part of the surface of the eyeball, has a 

 vertical slit just above the pupil, so that any encumbrance of vision is excluded. It seems 

 to me, on the contrary, that the purpose of this gelatinous scale is mostly to enlarge the 

 refracting parts of the eye, and to adapt the eye to the conditions of life in the deep 

 sea, as is probably the case with similar structures in other fish e. g. the herring, the 

 shad, the menhaden and others. It has been maintained, that this "scale" is enlarging 

 when the mackerel goes down to deep water, and is decreasing, when the fish rises 

 again; but a certain change in the appearance of the "scale" — if there exists any 

 change — is probably due only to the less or greater amount of fat deposited in the 

 orbital groove. 



A remarkable fact, which deserves to be mentioned, is, that a fish like the mackerel, 

 which is constantly changing its vertical range in the water, descending or rising, is 

 completely devoid of an airbladder, i. e. of an organ, which is generally considered as 

 being nearly indispensable for such vertical changes; and not less remarkable is the fact, 

 that a near relative of the mackerel, the so-called Spanish mackerel, — Scomber colias — 

 the biological peculiarities of which in many respects doubtless resemble those of the 

 common mackerel, has got an airbladder. 



A special chapter on the biology 01 the mackerel is formed by the discussion of the 

 spawning habits, the spawning times and places and the development of the eggs 

 and young. 



It is well known, that the mackerel approaching the coasts in spring-time, do so in 

 order to find convenient places for spawning, and that the floating eggs may really be 

 found — with few exceptions — in all regions, where mackerel are fished for, in the 

 months of May, June and July. This holds good for the American and for the North 

 European waters ; in the Mediterranean, as far as known, spawning begins and ends about 

 two months earlier. Especially the British waters, the North Sea and the Skager Rak, as 

 well as the American waters from Cape Hatteras to St. Lawrence Bay, may be considered 

 as spawning areas in all their parts, and from the reports available, it seems that in spite 

 of the widely differing conditions of temperature and salinity in these regions the spawning 

 process must be looked upon as a synchronous one. This, in my opinion, points very 

 decidedly to a common origin of the spawning schools, where equal conditions have been 

 ripening the sexual products simultaneously — whereas other species of fish, that occur 

 in the . same regions, in the North Sea as well as in the Channel, e. g. sole, sprat etc., 

 may differ in their spawning times by months. Nevertheless, it will be useful to corroborate 

 this conclusion, by exactly determining in different localities, how the spawning process 

 is developing; and the best means to do this will be, to examine by the well known 



