COMl'.\RATIVE STUDY OF SCOMBEOID FISHES. 365 



V.\SCÜLAR SYSTEM. 



In the vascuLix .^ysk^m too, we fiiiil iiuiuy voiy important points uf tlüTer- 

 ence among the scombroid fishes. Esixxjially the order Plecostci presents many 

 clmracteristic fcfttiiros, remiirknbly diflerent from nil the other fishes. ITio chief 

 features of difference are the gi-oater quantity of blood, greater number of blood- 

 vessels, and larger heart. Tlie most noteworthy (hfforence is the development 

 of the cutaneous vascular system, not found in the Teleostei, and peculiar vas- 

 <ular plexus iu the lateral muscle, iUid enormously developed vascular plexus 

 under the hver, or in the haemal canal. Therefore we distinguish three differ- 

 ent systems of blood-cii'culatiou in the Pleco^tei, namely vertebral, visceral, and 

 cutaneous. These three systt^ms luive respectively a peculiar feature in the 

 Plecostei ; but the peculiarity of the vertebral system is alternative with tliat 

 of the -visceral. Tlio cutaneous systam is very conspicuous and quite character- 

 istic to the Plecostei, and has a con-elation with the presence of the dark red 

 portion of the lateral muscle, roimd the vertebral column from the development 

 of sheet-hke vasailar plexus. It is very remarkable tlmt 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 Eiu'ope, 

 he did not put much weight on it, so that he desciibed it rather iu passing 

 in the following lines : — 



" Lorsqu'on a leve la peau du thon, on ti'ouve sous la ligne laterale 

 un gi'and vaisseau, qui donne de sa face externe, en dessus et en dessous, 

 beaucoup de branches dans les muscles voisins. Sa face interne est cri- 

 blee d'un nombre infini d'orifices d'autres branches, qui vont se perdro 

 sm- une membrane glanduleuse epaisse ". 



After CuviEB no one has studied nor even mentioned the pecuhar 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. IU, fig. 3); but identified them with prejudice as the 

 axial ai-teries, and did not trace fmihcr. In 1915 I published a paper on the 

 peculijir circulatory system (44) in the " Suisan Gakkwai Ho " (Procee<lings 

 of the Scientific Fishery Association) Vol. I, and in 1918 another paper m the 



