CHIEF CHARACTERS 



mv 



structure, yet their chief diagnostic characters may be summarised 



as follows : The dermal 

 ., dcv. skeleton is in the form of 



denticles and scales. There 

 are median fins supported 

 by endoskeletal radials (som- 

 actidia) ; and paired limbs 

 of similar structure. All 

 these limbs are fins adapted 

 to aquatic life, and have 

 the web strengthened with 



uv. 



VIV. 



FIG. 74. 



Transverse section of the trunk of Mustclut; 

 antarcticus, Gthr. (after T. J. Parker), showing the 

 veins, c, abdominal coelom ; cv, posterior car- 

 dinal ; (La, dorsal aorta; d.c.v, dorsal cutaneous 

 vein ; d.i.v, dorsal intestinal vein ; i.i.v, internal 

 intestinal vein at edge of spiral valve ; l.c.v, 

 lateral cutaneous vein; l.v, lateral vein; m.v, 

 elonic vein. 



Embryo of Gobius. (After Wencke- 

 bach, from Hertwig's Handbueh.) A, 

 aorta; //, heart; V.c.a, vena cardiualis 

 anterior ; V.si, vena subintestinalis ; D.C, 

 ductus Cuvieri. 



dermal fin-rays (dermo- 

 trichia). An elaborate 

 system of lateral-line 

 organs extends over the 

 head and trunk. The 

 heart retains an un- 

 divided atrium, and 

 pumps venous blood into 

 the branchial lamellae 

 of the gill-arches. Not 

 more than eight gill-slits 

 are pierced, of which the 

 first is tlie relatively 

 small spiracle. As char- 

 acters which are con- 

 sidered primitive, but 

 are often lost through 

 specialisation, may be 

 mentioned : an uncon- 

 stricted notochord, a 

 diphycercal tail, a large 

 number of radials in the 

 median and paired fins, an amphistylic attachment of the jaws, a large 



FIG. 76. 



Torpedo embryo with yolk-sac. (After Riickert, from 

 Hertwig's Handbueh.) 1, vitelline artery; 2, vitelline 

 vein ; 3, remains of the peripheral sinus. 



