OCR Text |
Show 1878.] MR. R. COLLETT ON CERTAIN GOBIOID FISHES. 325 teeth, which project very little beyond the jaws. Only the innermost part of the lower jaw is entirely toothless. These teeth make their appearance very early in the young. In a young specimen of scarcely 14 millims. length, some very minute (microscopical) teeth are already visible in the front part of the lower jaw, although they cannot with certainty be seen in the upper. In specimens of the total length of 23 millims. there are some small teeth visible in both jaws ; and on being dried, one may see that some of them are already developed; still they continue to be minute until the specimens have reached their full length. The teeth of the female undergo no special alteration the whole of their life through, but continue during the spawning-season in the same state as before; but in the males, on the other hand, these minute teeth of young specimens begin to disappear towards the spawning-season, and are replaced by a set of long and cylindrical ones. These long teeth do not proceed from the minute teeth, but constitute an entirely new set, which shoot forth at the same time as the orignal set disappears. In the specimens wherein the organs of generation are still not fully mature, both sets of teeth are visible for a short period at the same time, the new set only half developed. Finally, during the spawning-season all the minute teeth of the male have almost entirely disappeared, and are replaced by the new, long, and almost straight teeth, situated at a remarkable distance from each other, and chiefly to be found on the front part of the jaws. In the lower jaw their number is 4, or sometimes but 3, on each side; they are not particularly pointed, but almost cylindrical, only slightly curved, and placed almost vertically upon the outer edge of the jaw. At a little distance below and inside the last of these teeth, on each side, is found a sharp, curved tooth (canine) directed backwards and almost in the form of a claw. In the posterior half of the jaw the prolonged teeth are missing, a few of the minute teeth of the young period still remaining here. In the upper jaw the number of the long teeth is 5 on each side, of which a few (1-2) are also to be found behind the middle of the jaw. In the upper jaw there is also found, inside the ordinary row on each side, the curved canine, which is directed backwards; this canine is placed further in front than the opposite one in the lower, or nearly at the point of the jaw. There may further be found in the posterior part more or less remaining of the original minute teeth, whilst these only exceptionally are found at the point of the jaw. The fins.-The first dorsal fin has 5 rays, and is a little higher in the full-grown males than in the females, without, however, reaching the height of the body. All the rays are about evenly high, undivided, feeble, and rather closely set. This is one of those fins which appear latest, and is entirely wanting in specimens of a total length under 16 millims., wherein all the remaining fins have already got their rays. In individuals of the total length of about 22 millims. this fin is found with extremely feeble and short spines, which are often difficult to detect. |