31 



or the single eggs are fixed to the skin of the abdomen or 

 to the ventral surface of the tail and isolated in cutaneous 

 cells from their neighbours. The egg-plate is uncovered or the 

 eggs are enclosed in a pouch on the abdomen or on the tail, 

 formed by two folds of the skin, the free borders of which 

 remain at some distance from each other or meet in the median 

 line and may even coalesce. In the last case they open some 

 time after hatching, when the young are released. These folds 

 are reduced after the breeding season or they are permanently 

 closed to a sac with an anterior small opening (Hippocajnpus). 

 The skin-folds often also contain bony plates derived from 

 the body-rings, or these plates alone form the pouch-folds. 



Fig. 1 6. Dermal skeleton and pectoral arch of Siphoiiostoita fyphk I-. 



from outside, s superior, m median, / inferior lateral plates, sc scutelUim, 



fn praenucliale, n nuchale, cl cleilhrum, / pectoral, j jugular plates, 



c cover plate. (After Jungersen). 



Specialised fishes of small size living in the shore-water of 

 tropical and temperate seas; many species entering fresh water. 

 They are bad swimmers, moving about in a vertical position 

 by undulating movements of the dorsal. Those who are wanting 

 a caudal, are able to bend the end of the tail and to attach 

 themself by it to seaweed or other objects. 



Remarks: The discrimination of genera and species is in 

 the first place based on differences in the dermal armour, 

 constituted by bony scutes (shields or plates), arranged into 

 succeeding rings (annuli). 



In the praedorsal region each ring is composed of 7 plates : 



