2 ARKIV FÖR ZOOOGI. BAXD 7. N:0 25. 



classifioatory systems, not least on the Fishes, that we find 

 in the literature are illustrative examples hereon. I will end 

 this series of studies on the Plectognaths with a section in 

 which all the phylogenetical results attained independently 

 from the study of each organ will be discussed together. 

 From this, I think, it will then be possible to draw up the 

 main-lines of evolution that this fish-group has followed. 



Blood-vascular System. 



Our knowledge about the blood-vascular system of the 

 Plectognaths is limited to the short notices given by Hyrtl 

 (1851) on the renal system and adjacent blood vessels in 

 Diodon novemmaculatiis, Tetrodon maculaius and Triacanthus 

 hiaculeatus; by Ridewood (1899) on the efferent branchial 

 vessels and the circulus cephalicus in Balistes, Tetrodon, and 

 Orthagor isens, and by Milne-Edwards (1858) on the coronary 

 arteries in Orthagoriscus, the latter statements having been 

 recently controlled by G. H. Parker (1900), and notes about 

 the heart of Orthagoriscus by several authors. No description 

 of the whole vascular system in this Teleostean group has 

 ever been written. The contributions to the knowledge 

 thereof which I give below is chiefly based on studies of 

 Spher oides {Tetrodon) testudineus L. Unfortunately I ha ve 

 not had any fresh material at my disposal, but have been 

 compelled to dissect formol or alcohol specimens, besides 

 which I have been fortunate enough to get the oppurtunity of 

 making a series of microscopical sections through small specimens 

 of about 18 to 19 mm. in length (counted from snout to tip 

 of caudal fin). The specimens of the other Plectognaths that 

 I have dissected, viz. Diodon hystrix L. and liolacanthiis L., 

 Lactophrys trigonus L., Balistes vetida L., have not been pre- 

 served well enough to make it possible to give a complete 

 account of their vascular system, so I am able to make only 

 a few remarks about them. 



1. Heart. 



In the literature concerning the vascular system of the 

 Fishes I have not found any remarks at all on the heart of 



