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 larvae 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 larvae 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. — The 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 papillae. 

 This is the "integumentary vesicle" or "lymph-space" of Eyder, 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 arc now about 4*5 mm. long, and though their dis- 



