22 ARKIV FÖR ZOOLOGI. BAND 8. NIO 10. 



which is of ten divided in two or three »roots». Systematical 

 works contain several descriptions of varying forms of spines 

 and their arrangement. According to systematical descrip- 

 tions the integumental ossifications have not the shape of 

 spines in all species. Of Ephippion it is stated that »the 

 skin is armed with bony scutes forming a sort of carapace» 

 (Evermann). It would be of great interest to see the air-sac of 

 this genus, but nothing is known about it. Tetrodon guttifer 

 is also provided with a carapace according to Gunther's 

 Catalogue (Vol. 8, p. 273). It seems to me, that this cara- 

 pace cannot be well developed as Bennet, who was the first 

 that described this species, has, according to Gunther, over- 

 looked it. The species in question seems to be able to in- 

 fate the belly. The whole body is not covered with plates. 

 Perhaps represen ts this species a form in which the solid 

 mantle of plates or scales begins to dissolve. A detailed 

 study of the reduction of the integumental ossifications in the 

 Tetrodontids parallelly with the development of the air-sac 

 would without doubt be of great interest, but I have not 

 sufficient material of different genera and species for that 

 purpose. When the belly is inflated, the skin becomes ex- 

 tended. A consequence of this is that the spines, which in 

 the non-inflated state point caudally, become erected and 

 project a little more över the epidermis. The epidermis is 

 smoothed out. The bundles of fibres of the corium are 

 stretched. 



A study of the microscopic structure of the spines teaches, 

 that two portions can be distinguished as in the integumental 

 ossifications of all other Plectognaths, a homogeneous and a 

 fibrillated one. The former makes up the greater part of the 

 spine, the latter being only a comparatively thin layer at the 

 base between the roots. Fig. 14 shows the relation between 

 the two constituents of the spine. Dark and light zones can 

 be observed in the homogeneous part. The fibrillated part 

 consists of densified and calcified bundles of fibres without a 

 regular arrangement. 



To give a detailed account of the development of the 

 spines a series of several different stages of young specimens 

 would be necessary. To get sufficient material for this pur- 

 pose is most difficult. It is only a happy chance to catch 

 young specimens of the Tetrodontids. Such of a length of 



