274
J. H. 9. BLAXTER AND F. Q. T. HOLLIDAY
IV. THE LARVA
A. Development of organ system
The anatomy and development of the skeleton and organ systems
after hatching is best known in herring. At hatching the larvae vary in
length from 5-9 mm, the yolk being absorbed at 8-12 mm. The size of
the larva and its yolk supply and the rate of absorption of yolk depend
on the original egg size and race of the parents (Toom, 1958 ; Blaxter
and Hempel, 1963). The larvae of Sprattus aprattus, Sardina pilchardus
(Lebour, 1921) and h'urdinopa caerulea (Miller, 1952 ; Arthur, 1966),
however, hatch a t 3 4 mm and have used up their yolk at 6-6 mm.
I n herring larvae only a primordial fin is present at hatching in
addition to the pectorals ; the eyes are large, the mouth is non-functional
and the gut is straight. However, the jaw soon begins to grow forward.
At first the lower jaw does not articulate, being suspended by an elastic
ligament (Fluchter, 1963). Harder (1952) described the development of
the alimentary system, showing that the pyloric oaecae and caecum
gradually started to develop at about 25 mm, the liver already being
present. At this stage, too, the lateral musculature began to invest the
gut. Harder (1 960) also gave a comparative description of the development of the gut of many clupeids and related the gut proportions to the
cross-sectional area of the body and body mass.
Bamford (1941) studied the lateral line in herring which was completely developed a t 50 mm length. Sensory papillae are found in the
head region (de Kock, unpublished) of newly hatched herring larvae,
and over the body of Sprattus sprattus and Lsardina pilchrdzcs (Lebour,
1921). Holstvoogd (1957) described a well developed pronephros and
archinephric duct in herring larvae 10 mm long ; this is not present at
hatching (Holliday and Blaxter, 1961). Maier and Scheuring (1923)
quoted work on the development of the swim bladder and its mnnection with the labyrinth. At 7 mm the larvae had a much shortened
swim bladder rudiment and at 14 mm the connection with the labyrinth had already been established. The gill arches are present at
hatching but the gills are not functional until about 20 mm (Hazder,
1954). The blood contains a form of leucocyte but no erythrocytes.
The general development of the fins and skeletal system of herring
has been described by Lebour (1921), Schnakenbeck (1929), Buckmann
(1950), Blaxter and Hempel (1961) and Blaxter (1962). Wells (1922)
gave a description of the development of the chrondrocranium ; in the
newly hatched larva the ethmoid plate formed the roof of the buccal
cavity and the upper jaw (palato-pterygo-quadrate) began to develop
only at 13 mm. The detailed development of the vertebral column
J. H. 9. BLAXTER AND F. Q. T. HOLLIDAY
IV. THE LARVA
A. Development of organ system
The anatomy and development of the skeleton and organ systems
after hatching is best known in herring. At hatching the larvae vary in
length from 5-9 mm, the yolk being absorbed at 8-12 mm. The size of
the larva and its yolk supply and the rate of absorption of yolk depend
on the original egg size and race of the parents (Toom, 1958 ; Blaxter
and Hempel, 1963). The larvae of Sprattus aprattus, Sardina pilchardus
(Lebour, 1921) and h'urdinopa caerulea (Miller, 1952 ; Arthur, 1966),
however, hatch a t 3 4 mm and have used up their yolk at 6-6 mm.
I n herring larvae only a primordial fin is present at hatching in
addition to the pectorals ; the eyes are large, the mouth is non-functional
and the gut is straight. However, the jaw soon begins to grow forward.
At first the lower jaw does not articulate, being suspended by an elastic
ligament (Fluchter, 1963). Harder (1952) described the development of
the alimentary system, showing that the pyloric oaecae and caecum
gradually started to develop at about 25 mm, the liver already being
present. At this stage, too, the lateral musculature began to invest the
gut. Harder (1 960) also gave a comparative description of the development of the gut of many clupeids and related the gut proportions to the
cross-sectional area of the body and body mass.
Bamford (1941) studied the lateral line in herring which was completely developed a t 50 mm length. Sensory papillae are found in the
head region (de Kock, unpublished) of newly hatched herring larvae,
and over the body of Sprattus sprattus and Lsardina pilchrdzcs (Lebour,
1921). Holstvoogd (1957) described a well developed pronephros and
archinephric duct in herring larvae 10 mm long ; this is not present at
hatching (Holliday and Blaxter, 1961). Maier and Scheuring (1923)
quoted work on the development of the swim bladder and its mnnection with the labyrinth. At 7 mm the larvae had a much shortened
swim bladder rudiment and at 14 mm the connection with the labyrinth had already been established. The gill arches are present at
hatching but the gills are not functional until about 20 mm (Hazder,
1954). The blood contains a form of leucocyte but no erythrocytes.
The general development of the fins and skeletal system of herring
has been described by Lebour (1921), Schnakenbeck (1929), Buckmann
(1950), Blaxter and Hempel (1961) and Blaxter (1962). Wells (1922)
gave a description of the development of the chrondrocranium ; in the
newly hatched larva the ethmoid plate formed the roof of the buccal
cavity and the upper jaw (palato-pterygo-quadrate) began to develop
only at 13 mm. The detailed development of the vertebral column