8 ARKIV FÖR ZOOLOGI. BAND 8. NIO 10. 



bundJes of fibres running almost straight from one plate to 

 another and continuing into the bundles of the plates 

 (Fig. A). By this arrangement of the plates a complete 

 carapace is formed. 



The other genus belonging to this family, Ranzania, dif- 

 fers according to Steenstrup and Lötken from Mola, descri- 

 bed above, in having regular hexagonal plates. 



Development of integument. For a considerable time 

 several forms of small roundish fishes have been known and 

 described as a sort of dwarf-molids under different names. It is 

 only quite recently, that their true nature has been made clear 

 by Lutken and Steenstrup. The two Danish authors were 

 able to show a continuous series of forms representing different 

 stages of the evolution of a Mola. The youngest forms 

 known are provided with several very long spines. As the 

 young fish develops, the spines are reduced in length. The 

 above mentioned authors have followed this reduction of the 

 spines. In which way the reduction of the spines takes place 

 the above mentioned authors have not stated. I have had 

 an opportunity of examining some young fish having a length 

 of resp. 1,5, 3 and 5 mm. In all these specimens the epider- 

 mis is thin consisting of a few layers of cells, both mucous 

 and indifferent. The corium ist in mos t parts of the skin 

 already differentiated into the two layers described above, 

 the exteriör forming a loose reticulum and the interiör a 

 fibrillated one. The fibres are in these stages far less numer- 

 ous than in adult specimens, and the bundles do not show 

 the winding loop mentioned above as a character of this 

 layer of the corium. The integumental ossifications are com- 

 paratively few in number. They are almost all long spines 

 piercing the epidermis. The base of the spine forms a large 

 thin plate, concave on the under surface. Some plates carry 

 two spines. The plate is situated in the deepest part of the 

 exteriör layer of the corium. The spines with their extended 

 base are quite homogeneous. The fibrillated layer, which 

 forms the largest part of the plate in the adult specimens, 

 is not as yet developed. Except these rather few plates with 

 long spines giving the young Molids their characteristic spin- 

 ous shape, there is only a small number of integumental 

 ossifications in the stages examined. The greater part of the 

 skin is not as yet provided with any skeleton. These ossifi- 



