26 ARKIV 7 FÖR ZOOLOGI. BAND 8. N:0 10. 



are primitive Plectognaths, both groups separately spe- 

 cialized. 



From the description of the integumental ossifications it 

 will be seen, that the Plectognaths in this organ differ rather 

 much from the scales found in ordinary Teleosts. The ossi- 

 fications of the Plectognaths have another shape and are 

 not enclosed in pockets. This peculiar character has been 

 observed rather early. Agassiz who considered the superior 

 layer to be enamel referred the Plectognaths to the Ganoids, 

 an error which was corrected by Jon. Muller. The pre- 

 sence or absence of a layer of enamel is, however, of no im- 

 portance for the relation with the Ganoids, as these fishes 

 do not posses enamel on the scales. That there are many 

 characters in the structure of the integumental ossifications 

 comrnon to the Ganoids and the Plectognaths is certain, but 

 the main difference between the Ganoids and Teleosts is to 

 be found in other organs. Another point must be taken into 

 consideration. The »Ganoids» form without doubt no natural 

 group, they represent probably divergent branches of fishes. 

 The problem of the homology and phylogeny of fish-scales 

 is far from clear. There are about so many views thereof 

 as authors. A great number of different types of scales have 

 been described. I think that the fish-scales are much more 

 uniform than hitherto believed, but this question requires a 

 special inquiry. 



