72 ON SOME LARVAL STAGES OF FISHES- 



in five spots in the neighbonrhood of the yolk-sac. The largest of 

 these is not in the skin, but on the surface of the yolk-mass over 

 the oil-globule, which is situated at the posterior end of the yolk. 

 Another is at the base of the rudiment of the pectoral fin, pe. f. 

 Another is just behind the eye, and two others are at the anterior 

 end of the yolk-sac. 



The larva represented in fig. 5, Plate IV, is that of Gottus hubalis, 

 a species extremely common on the shore at Plymouth. The eggs 

 of this species are adhesive and are deposited in small rounded 

 clumps of about one and a half to two inches in diameter attached 

 to stones or rocks on the shore. There are usually numbers of 

 the fish in our tanks, where they regularly deposit their eggs. 

 The deposition of the eggs takes place in January, February and 

 March. The single egg is 1*7 mm. in diameter, and is characterised 

 by the presence of rounded protuberances all over the external 

 surface of the envelope. The yolk when the egg is first laid has 

 usually several rather large oil-globules, but during development 

 these coalesce into a single globule. Fig. 5 shows the appearance 

 and structure of the living larva immediately after hatching. The 

 larva is in a much more advanced condition than those of species 

 hatched from pelagic eggs. Its length is 5*7 mm. The mouth is 

 open and the cartilaginous branchial arches are already formed. The 

 choroid of the eye is fully pigmented, and has a deep blue colour 

 by reflection. Some of the yolk still remains and the oil-globule is 

 situated at its anterior surface. The condition of the heart is quite 

 different from that seen in newly hatched pelagic larvae ; instead of 

 a continuous perivitelline blood sinus, there are numerous definite 

 vitelline vessels, v. v., and in these, circulates fully developed red 

 blood, containing numerous red corpuscles. These vitelline vessels 

 lead to the posterior end of the heart, and in the opposite direction 

 are seen to be continuous with the vessels of the liver I. On the 

 dorsal side of the liver, in the figure, is seen the gall-bladder, con- 

 spicuous from the green colour of its contents. Above the liver is 

 seen the enlargement of the intestinal tube forming the stomach, 

 but the tube is without convolutions. The notochord is multi- 

 columnar, and below it are seen the caudal artery and vein, c. v., 

 in which the blood is seen in the living larva coursing in opposite 

 directions. The pectoral fin, pe. /., is large and membranous, 

 with a semicircular outline. The auditory vesicle with its two 

 calcareous nodules, and developing semicircular canals, is a con- 

 spicuous structure behind the eye. The distribution of pigment 

 in the larva is peculiar. Black pigment only is present, yellow not 

 being developed till a later stage. Pigment is altogether absent 

 from the caudal region ; the black chromatophores are almost en- 



