814 PROFESSOR W. C. M‘INTOSH AND MR E. E. PRINCE ON 
25th April.—Further changes occur in the pectorals which are bluntly lanceolate, 
and in the pigment which in the eye has a bright bronze-like hue. The urinary, vesicle 
and other viscera are advancing. 
The newly hatched cod float on the surface of still water. When a current of air is 
directed against them some wriggle aimlessly about, others, probably less robust 
specimens, float helplessly in the water. The yolk-mass is often uppermost, though some 
of the stronger carry it inferiorly. In many abnormal forms, which have a slightly 
distorted or curved appearance, the yolk lies laterally on the surface of the water. 
Four pigment-patches diversify the transparent body of the young larva, one behind 
the pectorals, one towards the posterior border of the yolk, and two on the tail. The 
disposition of these bands of pigment is well seen when the larve are placed in sea- 
water in a white porcelain vessel (Pl. XIX. fig. 8). The larval coloration is temporary, 
and differs in arrangement from that in the next and subsequent stages. 
27th April—the free larvee are very active, swimming forward in a straight course 
with considerable speed. When at rest, however, they often lie on the side, or float with 
the yolk uppermost. The snout has become free from the yolk-sac to some extent, and 
the oral aperture has burst through. The otocysts have approached the eyes. The yolk- 
sac is still large, but the breathing chamber anteriorly has expanded. The distinctive 
patches of pigment can now be made out on the trunk. In several advanced specimens 
the circulation was visible, the corpuscles passing along the dorsal aorta and returning 
after traversing about a quarter of the length of the tail. 
28th April.—The circulation can be traced two-thirds along the tail, and though a 
definite branchial circulation cannot be made out, a confused movement of corpuscles 
having the appearance of a plexus occurs posterior to the otocysts. The larval cod swims 
in straight lines, and now keeps the yolk-sac inferior. 
29th April.—The general outline is altered, the upper jaw projects beneath the eye, 
and a depression divides it from the olfactory enlargement superiorly. The mandible 
extends a little beyond the upper jaw. The yolk-sac has much diminished, the folds of 
the mesenteron have increased, and the branchial system become more complex, while 
the aorta proceeds almost to the tip of the tail. 
30th April.—tThe dorsal median fin now begins over the mid-mesenteric region, and 
the cuticular tissues in front form an expanded cap over the head, covered with papille. 
This is the “integumentary vesicle” or ‘lymph-space” of Ryprer, who mentions 
homologous structures in the Spanish mackerel and other forms. He does not now 
consider this as an extension of the median dorsal fin-fold, which is never carried to the 
front of the head. It is very characteristic of the gadoids as well as of several 
pleuronectids. 
1st May.—The development of the pectorals is marked, and they are slightly angular 
in front, rounded posteriorly. They are brought to the sides, and by a wriggle of the tail 
the fish progresses. 
2nd May.—The larval cod are now about 4°5 mm. long, and though their dis- 
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