10 ARKIV FÖR ZOOLOGI. BAND 8. NIO 10. 



Mola the epidermis does not touch the spines. The exteriör 

 layer of the corium forms processes in the epidermis, one for 

 each branch of the spine. The epidermis has nothing to do 

 with the formation of the spines. The development of the 

 integumental ossifications and their growth according to the 

 opinion here put forth is diagrammatically shown in Fig. B 

 and C. There is another point in the development of the 

 ossifications which has not yet been discussed. In what 

 manner does the reduction of the long spines characteristic 

 of young specimens of Mola take place? Lutken and 

 Steenstrup have only stated the reduction. The stages I 

 have had at my disposal do not give any hints as to the 

 settling of this question. 



Subcutaneous tissue. Inside of the thick layer of strongly 

 fibrillated connective tissue forming the interiör stratum of 

 the corium a thin layer of subcutaneous tissue has been 

 developed. 



Ostraciontidae. 



The species belonging to this family, the trunkfishes, are 

 well known by the carapace formed by the hexagonal, juxta- 

 posed bony plates of the skin. The shape of the carapace 

 varies considerably and forms an important specific charac- 

 ter. The plates are covered with small tubercles, in some 

 species a few plates also exist with large spines. William- 

 son has given a detailed description of these plates, which, 

 however, is quite erroneous in many respects. My studies 

 on the integument of this family are based on full grown 

 specimens of Ladophrys trigonus L., but there is no reason 

 to believe that other forms show any differences of impor- 

 tance. Unfortunately I have not had an oppurtunity of 

 examining young specimens. After an account of the results 

 of my own studies I shall make some criticisms on Wil- 

 liamson's opinion concerning the structure of the plates. 



Epidermis. The epidermis is thin, containing only a 

 few layers a cells. 



Corium. Two different layers of the corium can be 

 distinguished: one exteriör, forming a very thin stratum be- 

 tween the epidermis and the plates, and one interiör. The 



