ARKIV FÖR ZOOLOGI. 



BAND 7. N:o 30. 



Studies on tlie Plectognaths. 



2. The Air-sac, with notes on otlier parts of the intestiiies. 



By 



NILS ROSÉN. 



With 2 Plates and 7 Figures in the Text. 



Communicated February \\^^ 1912 by Hj. ThÉel and E. Lönnberg. 



Although the power of inflating the belly that many 

 Plectognaths possess has been known for a verv long time, 

 this pecub'arity has hardly been studied. Except a few notes 

 by earlier authors, our knowledge about this question is Hraited 

 to the short papers written by W. Sörensen and O. Thilo. 

 The former writer describes mainly the muscles of Tetrodon 

 fahaka Hasselquist, giving only sorae remarks about the form 

 of the air-sac (»Oppustningssaekken») in this species, together 

 with a far from happy explanation of the nature of this or- 

 gan. Thilo, on the other hand, has made rather interesting 

 studies, but the chief point of interest for him has been 

 the mechanism of the pectoral and pelvic bones and their 

 relations to the inflating power. Many of the most interesting 

 problems about the air-sac, viz. its structure in different 

 species and genera, its homology, development and function 

 are far from thoroughly worked out. It is quite probable 

 that the great alteration of the form of the body which is 

 caused by inflating the belly has influenced the structure of 

 several organs. All these questions I shall deal with in this 

 paper, as far as the material at my disposal will allow. The 



Arkiv för zoologi. Band 7. N:o 30. 1 



