NILS ROSÉN, STUDIES ON THE PLECTOGNATHS. 19 



Hyrtl gives a few notices about the venous system of 

 the kidneys in Diodon novemmaculatus, Tetrodon macidatus 

 and Triacanthus hiaculeatus. In all he has found that the 

 posterior cardinal vein runs for a rather long distance unpair- 

 ed, then divides in two branches which break up entiiely 

 into a capillary system in the kidneys. 



As our knowledge about the vascular system of the 

 Teleosts is very limited, it is rather difficult to say what is 

 primitive or not in the arrangements of the vessels. In a few 

 cases, e. g. circulus cephalieus and the branchial arteries, we 

 know a little more. As pointed out in the introduction, it 

 is a great mistake to try to make a classification based on 

 only one anatomical system. The reason therefore is, of 

 course, that the same shape of an organ, the same arrange- 

 ment of a vessel and so forth may very often have been 

 obtained on separate lines of evolution. I think that the 

 form of the circulus cephalieus and its relationship to the 

 efferent branchial arteries, as mentioned above, illustrate this 

 in an excellent manner. In the last number of this series of 

 studies on the Plectognaths I shall discuss the phylogeny of 

 this fish-group, taking all the systematically important organs 

 into consideration. Here I shall only give a few remarks 

 about the conclusions that may be drawn from the studies 

 on the blood vascular system. 



On taking a general view of the results obtained there 

 is something that we from a phylogenetical point of view at 

 once observe the occurrence of a great number of both primitive 

 and highly specialized characters not only witliin the group but 

 also in the same form. As primitive conditions we may con- 

 sider the great number of valves between the auricle and 

 ventricle and in conus arteriosus in Orthagoriscus, the origin 

 of the coronary arteries in the same form, the small circulus 

 cephalieus and the arrangement of the efferent branchial 

 arteries in Lactophrys and Balistes. Whether the existence 

 of lateral veins is to be regarded as primitive cannot be decid- 

 ed before other Teleosts have been studied on this point. We 

 find specialized characters in the large circulus cephalieus in 



