1214 
SCANDINAVIAN FISHES. 
one, which is said to have its roots in the capillaries of 
the intestinal canal, runs under the stomach and caecum, 
there ramifying into a capillary network between the 
green cells in the wall of the caecum, which is said to 
functionate as a kind of liver. Here the blood, it is 
stated, is again collected, on the upper side of the cae- 
cum, in the other, superior canal, whose contractions 
run backwards in the opposite direction, to the exit of 
the caecum from the stomach, and convey the blood to 
the heart: — and we should thus have found here a 
portal vein (the inferior canal) and an efferent hepatic 
vein (the superior canal). Descriptions have besides 
been given of a separate, but wall-less lymphatic system, 
tilling all the cavities of the body and ramifying into 
the smallest lacume between the organs. But in all the 
said contractile canals there appear distinct traits of the 
typical arrangement of the vessels in a worm. In those 
paired connecting vessels between the upper vessel and 
Fig. 370. Anterior end of a Branchiostoma lanceolatum , seen from 
the right and magnified. After Vogt and Yung. 
a , olfactory depression; b, first, c, second pair of nerves; d , eye spot; 
e, peripheral ganglion cells in the skin; /, notochord; g , spinal cord; 
h , fin-ray growths (spinous processes?); i , myocomma. 
the lower which are most plentiful in the forepart of 
the worms ( Annulata ), we may well seek a parallel to 
the respiratory system of Branchiostoma. And the two 
contractile vessels that run bulging in the latter along 
the upper and lower sides of the intestinal canal also 
functionate in the worm for the first sucking up of the 
alimentary juice and its conversion into nutritive fluid. 
The vertebral segmentation of the body is indeed 
subindicated even in Branchiostoma by a transversal 
division of the membrano-cartilaginous sheath that en- 
velops the notochord, expands both around the neural 
0 Monatsber. Akad. Wiss. Berlin, 1839, p. 198. 
b Mull. Arch. Anat., Physiol., 1843, p. 32. 
c Ann. Sc. Nat., ser. 3, Zool., tome IV (1845), p. 226. 
canal and the h genial cavity, and breaks up at the base 
of the vertical dermal fin-fold along the dorsal and the 
posterior part of the ventral margin into pieces resem- 
bling fin-rays (fig. 364, a and h ; fig. 370, h) — though 
far more numerous than the muscle flakes. But the 
muscular and nervous systems are the organs that here 
most distinctly call to mind the vertebrate type. 
That portion of the muscular system which answers 
to the great lateral muscles of fishes is divided into 
transverse bands ( myomeres ), which are angular, with 
the angle directed forwards; and each myomere is com- 
posed of bundles of muscle fibre extended between ten- 
dinous expansions of the notochordal sheath ( myocom - 
mata), just in the manner of the said piscine muscles. 
Along' the ventral side of the abdominal region, between 
the mouth and the atrial pore, extends an horizontal 
muscular plate, composed of transversal muscle fibres. 
Its function, consisting of rhythmical contractions, is 
mainly subservient to the respiration, and its posterior 
part, at the atrial pore, swells into the so-called abdo- 
minal papilla, coursed by muscle fibres in all directions. 
The nervous system shows the peculiarity that the 
spinal nerves (except the first two pairs) do not. issue 
in pairs, exactly opposite each other, but alternately, 
the nerves of one side in front of those of the other 
(fig. 366, e), and that only the basal parts of the dorsal 
branches (sensory nerves) are entire, those of the ven- 
tral (motory) nerves being broken up into fibres. In 
the spinal cord there appear, as in the preceding order, 
besides the ordinary ganglion cells, large so-called co- 
lossal cells. Among the organs of sense A. Retzius was 
the first" to discover a black pigment spot (fig. 370, d) 
on the anterior end of the spinal cord. This spot is 
interpreted as an eye of the most rudimentary descrip- 
tion. It is comparatively larger in young specimens 
than in old, which suggests a still advancing reduction; 
and its visual function is somewhat dubious, for similar 
spots also occur in a row on each side along the greater 
part of the spinal cord. Above the anterior end of the 
spinal cord, but on the left side of the body, Kolliker' 
and, after him, Quatkefages 0 found a ciliated depres- 
sion (fig. 370, a), the simplest form of an olfactory 
apparatus. The organs of taste we have already re- 
marked on the cirri of the mouth aperture and the 
postoral velum; and a similar cell structure also appears 
