of the Fishery Board for Scotland. 



207 



in contrast with their general blackish dusting. The circulation was 

 complete, and in full activity. 



In contrast with the young four-bearded rockling of exactly the same 

 length, the eye is brownish instead of bluish-black, and silvery, — a feature, 

 however, to which no weight need be attached. No pigment occurs on 

 the body, but the ventral fins are brownish throughout, and much shorter 

 than in the other species. The snout is less blunt and heavy than in the 

 four-bearded form, — a feature partly due to its diminished diameter. 



At 16*5 mm. a large barbel occurs at the tip of the mandible, and 

 short processes at the anterior nostrils, as well as traces of the labial 

 barbels. The pectoral fins are considerably elongated, though they have 

 not reached as far back as the tips of the ventrals. The body is silvery, 

 with the exception of a small portion at the tail, and with dark pigment 

 at the dorsum. The tail is symmetrical, so that the curve of the notochord 

 would seem to be temporary. 



A young parasite (C aligns) had fixed itself over the cardiac region. 



At 24 mm. (Lochmaddy, in August), the characters are quite evident, 

 viz., the presence of five barbels, the largest being that on the chin, and the 

 last developed being the pair on the lips, the character of the head, and the 

 greater depth of the trunk immediately in front of the caudal fin. Day 

 states that the young of this form is brown, with blue eyes ; but not a few 

 of the length just mentioned, and larger, have the steel-blue of the 

 dorsum, and the silvery sides so characteristic of the four-bearded species 

 (Onos cimhrius). Perhaps, however, Dr Day alludes to a later stage, 

 and variations may occur in regard to the assumption of the adult 

 characters. The first ray of the dorsal is not much thickened in these 

 bluish silvery pelagic forms. 



When 28*5 mm. long, on the 9th of June, an example showed that at 

 this stage variation also occurred, since the labial barbels were just 

 indicated, and no more. The dorsum was not so deeply pigmented as in 

 some, but the whole fish was silvery. The filament of the first dorsal 

 fin was long. The ventrals were still long, though proportionally shorter 

 than in the early stages, being apparently about a seventh the length of 

 the body, and with black pigment at the tip. 



One at 30 mm., in August, had so far altered its habit as to be found 

 amongst muddy sand — when digging for littoral annelids at Lochmaddy, 

 North Uist. Its more sober hue, deeper body, longer fins, and less 

 attenuated form at once distinguished it from the preceding stage. The 

 dorsum was of a dull green, dotted with black — merging inferiorly into 

 the silvery lustre of the sides ; though, towards the tail, the dull green 

 again predominated. The cheeks behind the eyes were silvery, dotted 

 with black ; the black chromatophores, indeed, occurred over the entire 

 body, with the exception of the anterior part of the abdomen, which was 

 silvery, with a bluish-green iridescence. The irides were greenish-blue. 

 In spirit, the colour of the dorsum became russet-brown, and a faint 

 brownish hue appeared on the sides. The pectoral fins were kept in 

 rapid vibration, and the first dorsal had the usual active ciliary motion. 

 The first ray of the latter had a probe-point. The head had now assumed 

 its characteristic proportions. The barbels were longer. The pelvic 

 fins were still long ; while the tactile extremities of the four anterior rays 

 — especially the separate tips of the first and the second — were better 

 developed, probably in connection with the change of habit. 



A series of pelagic specimens, captured between the 6th and 27th of 

 October, show that, in this species, the dark dorsum and silvery sides are 

 characters pertaining to pelagic life ; and, moreover, that some pursue 

 this habit longer than others, or at least attain a considerably larger size 



