COMPARATIVE STUDY OF SCOMBROID FISHES. 
365 
VASCULAR SYSTEM. 
In the vascular system too, we find many very important points of differ¬ 
ence among the scombroid fishes. Especially the order Plecostei presents many 
characteristic features, remarkably different from all the other fishes. The chief 
features of difference are the greater quantity of blood, greater number of blood¬ 
vessels, and larger heart. The most noteworthy difference is the development 
of the cutaneous vascular system, not found in the Teleostei, and peculiar vas¬ 
cular plexus in the lateral muscle, and enormously developed vascular plexus 
under the liver, or in the haemal canal. Therefore we distinguish three differ¬ 
ent systems of blood-circulation in the Plecostei, namely vertebral, visceral, and 
cutaneous. These three systems have respectively a peculiar feature in the 
Plecostei ; but the peculiarity of the vertebral system is alternative with that 
of the visceral. The cutaneous system is very conspicuous and quite character¬ 
istic to the Plecostei, and has a correlation with the presence of the dark red 
portion of the lateral muscle, round the vertebral column from the development 
of sheet-like vascular plexus. It is very remarkable that such a conspicuous 
and peculiar system of circulation remained almost unknown to science. Though 
the keen eyes of Cuvier (12) discovered it in the common tunny of Europe, 
he did not put much weight on it, so that he described it rather in passing 
in the following lines :— 
“ Lorsqu’on a levé la peau du thon, on trouve sous la ligne laterale 
un grand vaisseau, qui donne de sa face externe, en dessus et en dessous, 
beaucoup de branches dans les muscles voisins. Sa face interne est cri¬ 
blée d’un nombre infini d’orifices d’autres branches, qui vont se perdre 
sur une membrane glanduleuse épaisse ”. 
After Cuvier no one has studied nor even mentioned the peculiar blood¬ 
vessels. In 1836, Eschricht and Müller (19) published an interesting paper 
on the peculiar plexus of blood-vessels among the viscera of the common 
European tunny. In that paper they give a figure, showing the origin of the 
cutaneous arteries (Taf. Ill, fig. 3); but identified them with prejudice as the 
axial arteries, and did not trace further. In 1915 I published a paper on the 
peculiar circulatory system (44) in the “ Suisan Gakkwai Hö ” (Proceedings 
of the Scientific Fishery Association) Vol. I, and in 1918 another paper in the 
