N. ROSÉN, STUDIES ON THE PLECTOGNATHS. 3 



is characterized by cells of connective tissue formin g a loose 

 reticulum. The fibres are few. The blood-vessels are numer- 

 ous. Along the basal membrane there is a series of pigment 

 cells, which give the skin of Mola a brownish colour. The 

 interiör layer of the corium is quite distinct from the exteriör 

 one and is the part of the skin which has been described 

 by earlier authors. As already mentioned, the best account 

 thereof has been given by Turner. Låter authors have 

 added nothing new to this. The layer in question is very 

 thick, pure white and of a härd structure. Turner has prov- 

 ed by chemical and microscopic investigations, that this 

 layer consists solely of connective tissue with neither fat 

 nor elastic fibres. 1 The studies I have made on the struc- 

 ture of the skin of Mola have given quite the same result 

 in this point. There is no trace of fat cells. The fibres were 

 all stained red by van Gieson's mixture showing their col- 

 lagen nature. Kresofuchsin, which in alcoholic solution is a 

 good reagent on elastic fibres, had no effect whatsoever on 

 them. Turner considered the fibres to be specially peculiar 

 in not being collected in fibrillated bundles, but it seems 

 to me that Turner has mistaken the bundles of fibres for 

 the fibres themselves. The fibres are very thin, collected in 

 bundles which anastomose with each other. The bundles have 

 a curling tortuous course and run close to each other. Owing 

 to this arrangement of the bundles of fibres this part of the 

 corium gets its characteristic härd structure. Fig. 6 on 

 plate II shows a microphoto of part of a microsection through 

 this peculiar stratum magnified 200 times. The cells are 

 very small. The blood vessels are few compared with their 

 abundance in the exteriör layer of the corium. The limit 

 between the two layers of the corium is formed by the 

 plates. 



Ossifications. The integumental ossifications of Mola 

 have the form of irregular plates serrated at their margins 

 (Fig. 3). From the centre of the plate a large spine projects. 

 Sometimes the plates carry two or several spines. The spine 

 is not a simple one. Several long and narrow branches 



1 In the recent interesting work »Atlanterhavet» Hjort has quite 

 overlooked this fact and speaks about a layer of fat which diminishes 

 the specific weight of Mola rendering the pelagic life of this fish possible. 

 This opinion is quite erroneous. 



