The present investigation was undertaken at the invitation of H.M. Treasury, in consequence of an application to the government from H.M. Inspectors of Irish Fisheries for a scientific investigation into the life-history of the mackerel. The problem to the solution of which the inspectors attached particular importance was the relation to one another of the spring and autumn schools of mackerel which regularly visit the Irish coasts. In the spring a multitude of large fish approach the south and west coasts of Ireland to breed. In the autumn schools of immature, but usually well-grown, mackerel come around the island. According to one of the inspectors, the Rev. W. S. Green, there is a sharply defined interval between the two visitations of fish.

The investigations dealt with in this memorandum were commenced in the autumn of 1895, and have been carried on, as opportunity permitted, until July of the present year. The observations were made in 1895 and 1896 by Mr. F. B. Stead, in 1897 by Mr. S. D. Scott and myself, and in 1898 by myself. A preliminary memorandum, dealing with the observations made in 1895, has already been submitted to the Committee by Mr. Stead. As a matter of general convenience it is reprinted as an appendix to this Report.

In the following Memorandum I propose to lay before the Sub-Committee of Enquiry, appointed by the Devon Sea Fisheries Committee, certain facts with regard to the contents of two of the bays on the South Coast of Devon, in which I have conducted trawling experiments, and then to point out the bearing of these facts on the practical questions before the Committee.

A Pontobdella lived in my tanks for about six months of the present year. I first placed it in a wide shallow tank with a variety of Actiniæ and a few Hermit Crabs, but no fish of any sort. When first introduced the leech was very restless, and wandered all over the tank. After a day or so, however, he took up his abode on the glass, close to the surface. He remained in this spot about three months, and if disturbed would always go back to it. He never noticed any of the other animals, and did not appear in the least sensitive to the stinging power of the tentacles of the Actiniæ. I have frequently seen him plunge his head and neck in amongst the tentacles of a large Anthea cereus who lived near him, and he treated T. crassicornis with a like disrespect.

So soon as the weather grew warm, the leech displayed signs of uneasiness, and finally left his place on the glass, and retired to a cool corner formed by the slate back and side of the tank, close to the syphons of the aerating apparatus, where he remained two months and a half.

He never appeared to notice sticks or nets moving near him in the water, but would remain in his usual position, viz., the base fixed to the wall of the tank, the body sticking out horizontally for about half its length, and the fore part doubled under, so that the mouth was pressed against the under side.

Morone labrax. Linn. Bass.

Towards the end of May a large female bass in one of the Aquarium tanks appeared to be approaching ripeness, and constantly swam round the tank followed by one or more of its companions, probably of the opposite sex. A fine-meshed net was accordingly placed over the overflow from the tank in question, and on the morning of the 29th May was found to contain a very large number of eggs, undoubtedly attributable to this species, the only other Teleostean inmates being turbot, congers, pollack, rocklings, and two species of wrasse.

All the eggs proved to be unfertilised, or, at most, showed only an approach to segmentation, which may have been due to the spermatozoa of a rockling. Circumstances seemed strongly to point to the fact that the eggs are not all shed at once, but owing to an unfortunate series of accidents with the net it is impossible to speak on this point with absolute certainty.

Although the bass is a common British fish, its ova find no place in the records of British naturalists, and are only known from the descriptions of Raffaele, who obtained them both from parents living in the tanks of the Naples Laboratory and from the neighbouring sea.

The eggs observed by us at Plymouth are spherical, and, while living but unfertilised, measure from 1·25 to 1·34 mm in diameter. Raffaele gives 1·155 to 1·2 mm as the diameter of Naples examples. The latter have an oil-globule of ·332 to ·366 mm.

By the kindness of Mr. J. Jacobs, to whom the Laboratory is already indebted for many specimens of interest, I received on the 15th June a fine example of the species mentioned above, which had been trawled off the south coast of Ireland. The fish weighed 1 lb. 5 oz., and measured 42 cm., or 16½ inches. Though taken at least a day previously, it was in excellently fresh and firm condition. I have already recorded its capture in a letter to the Field and at a meeting of the Zoological Society, but the locality was inexactly given in each of these communications. I have since learned that the correct locality is 50° 20′ N., 8° 25′ W., or about seventy-five miles true S. of the Old Head of Kinsale, depth seventy-four fathoms. A number of the same species were trawled, and some were found to be excellent eating. I have no means of deciding whether the occurrence of A. silus on the ground indicated is normal or exceptional. If it can be taken in any quantity it should prove a valuable addition to our list of food-fishes.