of the Fishery Board for Scotland. 



223 



The yellowish hue was more distinct on the 30th March. On the head 

 it was somewhat diffused, as the chromatophores had given off branches. 

 The rows of rounded specks along the sides were only faintly tinted 

 (PI, VI, fig. 9). Both yellow and black pigments were present. The 

 latter (black) were very finely ramose on the dorsum of the snout and 

 on the head, as well as behind the otocysts. Distinct muscular twitchings 

 of the body occurred to-day. 



On the 1st April, the embryo more than stretched across the egg (PI. VI. 

 fig. 10) ; but in most the pigment-corpuscles remained simple. The heart 

 was minutely papillose internally and trumpet-shaped. Slow contractions 

 occurred at intervals. Most of the yolk was absorbed, and the alimentary 

 canal formed a pale band in front. The otocysts sometimes differed in size. 

 The day after, most of the yellow chromatophores in some were ramified, so 

 that the colour was diffuse, but in others the pigment-specks remained 

 circular. A few small black points were mingled amongst the yellow 

 along the sides of the body. At this stage the yolk was quite free from 

 pigment. 



A few were hatched on 3rd April, and many next day. It is possible 

 that the conditions as regards still water and low temperature may have 

 considerably delayed hatching. A specimen removed from the capsule 

 on the latter date (4th April, PI. VI. fig. 11) differs in some respects from 

 that figured by Mr Holt, viz., a larva about half a day old, since the pig- 

 ment is not definitely marked in his sketch. Moreover, the former pre- 

 sented no embryonic rays in the caudal ; indeed, these did not appear for 

 some time. Mr Holt's specimens therefore were probably more advanced 

 at the period of hatching. No mouth is visible, and the esophagus ends 

 blindly in front. With the exception of those on the head, the yellow 

 chromatophores are still rouuded, though, as a rule, the pigment is branched 

 at or shortly after hatching. In a lateral view, the yellow chromatophores 

 are grouped chiefly at the dorsal and ventral margins of the muscle-plates, 

 and on the rectum ; the tip of the tail is devoid of them. Besides the 

 yellow, very finely ramose black pigment-corpuscles occur on the head, 

 and amongst the yellow along the body, but it is not easily seen after the 

 yellow chromatophores become stellate, and in some specimens it is late 

 in appearing. The upper part of the head is chiefly occupied by black 

 pigment. A change must thus ensue before the pigment is grouped into 

 bars, for it is somewhat general at this stage. The lumen of the gut has 

 not entered the oblique portion of the rectum, and the pre-anal region of 

 the marginal fin is small at this stage. A more advanced condition of 

 the pigment is shown in a specimen (also removed from the capsule) on 

 the 5th April. Both yellow and black chromatophores are finely branched 

 (PI. VII. fig. 1 ). The variability in regard to the development of the pig- 

 ment is further shown in the sketch of an example three days later, viz., 

 8th April, in which the pigment has now been grouped in bars, — that is to 

 say, at certain parts the extension of the chromatophores is more pro- 

 nounced than at others (PI. VII. fig. 2). Thus the head and the region of 

 the body-proper have yellowish and black pigment, the latter along the 

 dorsal and ventral edges of the muscle-plates, with a special area at the 

 rectum, and three bars behind the latter, that near the tip of the tail being 

 mostly black, though a few yellow chromatophores are present. The eyes 

 also have pigment-specks ; the caudal shows embryonic rays. Tho yolk 

 has considerably diminished. The otocysts are still elongated from before 

 backward, but present a double outline from the differentiation of the 

 capsule. 



The larvae daily increased in activity and size, and the five groups of 

 chromatophores became very distinct, viz., one on the body over the 

 middle of the yolk, another at the rectum, two conspicuous bars behind 



