190 ZOOLOGY SECT. 



in the adult Callorhynchus, but in the young (Fig. 853) the 

 extremity of the tail proper is not upturned, and the fin-rays are 

 arranged symmetrically above and below it, producing the form 

 of tail-fin called diphycercal. In Chimsera the dorsal lobe of the 

 tail may be produced into a long whip-like filament (c.f.). The 

 pectoral {pct.f.) and pelvic (pv.f.) fins are both large, especially 

 the former. 



In the male there is a horizontal slit {B, a. cl.') situated a little 

 in front of the pelvic fins ; it leads into a shallow glandular pouch, 

 from which can be protruded a peculiar and indeed unique 

 apparatus, the anterior clasper (A,a.cl), consisting of a plate 

 covered with recurved dermal teeth, to which is added, in Callo- 

 rhynchus, a plate rolled upon itself to form an incomplete tube. 

 The use of this apparatus is not known. A rudiment of the pouch 

 occurs in the female, although the clasper itself is absent. The 

 male possesses, in addition, a pair of the ordinary pUrygopodia or 

 posterior claspers {ftg.), and is furthur distinguished by the 

 presence of a little knocker-like structure, the frontal clasper (fr. cl.), 

 on the dorsal surface of the head. In Harriotta the claspers are 

 poorly developed, and the frontal clasper is absent. 



The lateral line (I. I.) is an open groove, and there are numerous 

 sensory pits, arranged in curved lines, on the head. The skin is 

 smooth and silvery, and bears for the most part no exoskeletal 

 structures. There are, however, delicate, recurved dermal teeth 

 on the anterior and frontal claspers, and the first dorsal fin is 

 supported by an immense bony spine or dermal defence [sp.). In 

 the young, moreover, there is a double row of small dermal teeth 

 along the back. 



Bndoskeleton. — The vertebral column consists of a persistent 

 notochord with cartilaginous arches. In Chimaera there are 

 calcified .rings (Fig. 848, c. r.) embedded in the sheath of the 

 notochord. The anterior neural arches are fused to form a 

 high, compressed, vertical plate, to which the first dorsal fin 

 is articulated. The cranium (Figs. 849 and 850) has a very 

 characteristic form, largely owing to the compression of the 

 region between and in front of the large orbits, which are 

 separated -from the cranial cavity only by membrane in Callo- 

 rhynchus (Fig. 850, or.); in Chimsera they lie above the level of 

 the cranial cavity and are separated from one another by a median 

 vertical partition of fibrous tissue (Fig. 849, i. o. s). At first 

 sight the palatoquadrate, or primary upper jaw, appears to be 

 absent, but a little consideration shows it to be represented by a 

 triangular plate (2^al. qu.) which extends downwards and outwards 

 from each side of the cranium and presents at its apex a facet for 

 the articulation of the mandible. The palatoquadrate is therefore 

 fused with the cranium and furnishes the sole support for the lower 

 jaw; in a word the skull is aittostylic. The pituitary fossa (Fig. 



