ARKIV FÖR ZOOLOGI. 



BAND 7. N:o 25. 



Studies 011 tlie Plectogiiatlis. 



1. The Blood-vascular System. 



By 



NILS ROSÉN. 



With 2 Piates and 10 Figures in the Text. 



Communicated December 6th 1911 by H. Theel and E. Löxnberg. 



With this paper I begin to publish a series of studies 

 on the anatomy of the Plectognaths. The leading points of 

 view in them will be partly the peculiar power of inflating 

 the belly that many of these fishes possess, the anatomical 

 structures that render this possible, the modifications in the 

 shape and situation of several organs that have been caused 

 by this, and partly the phylogeny. After each account of 

 the different organs short remarks will be given as to the 

 way in which the evolution of the Plectognaths seems to 

 have proceeded when we have to explain the variations shown 

 by the organ in question. To base the building up of a 

 phylogenetical tree solely on one anatomical system is a great 

 error which far too many anatomists commit. What verv 

 often seems to be the most minute series of different stages 

 in the development of a structure, is, I am quite sure, in 

 many cases the results of an evolution on different lines. 

 By means of convergence or parallelism the same shape of 

 an organ may be obtained. To decide whether certain ana- 

 tomical structures are stages in the same line of evolution 

 or not, is therefore a question that very often cannot be 

 settled without also a study of other systems. The numerous 



Arkiv fur zoologi. Band 7. X:o 2'». 1 



