DESCRIPTION OF AN ANTARCTIC SPECIMEN 7 



minent feature. This tentacle is derived from the modified front portion of the dorsal fin. Kroyer 

 (1844) considered that in Ceratias it represented the first dorsal fin ray. Later authors (Brauer, 1908; 

 Waterman, 1948) working on Gigantactis, have concluded that a rudiment of the second fin ray also 

 enters into its structure. 



In the Ceratiidae the cephalic tentacle achieves its most considerable development as an angling 

 device. Here the first external ray of the fin, called the illicial ray or illicium, is suspended in front of 

 the head upon an exsertion of the pterygiophor or ' basal bone ' of that ray. The distal end of the illicium 

 is expanded into a luminous bulb, so that this apparatus projecting from the head is virtually that of 

 a fishing rod, line and bait. The cephalic tentacle of the new specimen is a stiff, slender rod which, when 

 found, extended at an angle of 20 to the horizontal and protruded 15 cm. from its insertion on top of 

 the head above the vestigial eyes. The illicial ray was jointed to its distal end and measured 6 cm. 

 (PI. I). 



Waterman (1939a) has pointed out that it was Reinhardt (1837), describing Himantolophus, who first 

 implied that the illicium functions as a lure. Later this was definitely asserted by Lutken (1871). The 

 luminosity of the bulb, or ' esca', in certain Ceratioidea was first mentioned by Willemoes-Suhm (1877). 

 In 1878 Gill independently suggested that the bulb was a luminous organ, and intimated its significance 

 as a luminous bait for the lure. The bulb has been credited with other functions. Thomson (1877) 

 described the illicium of Ceratias uranoscopus and favoured the belief (which may be partially true) that 

 the terminal bulb is a sense organ, informing the angler fish of the approach of prey, rather than a lure 

 to attract it. Goode (1880) and Goode & Bean (1895) expressed a similar opinion. A modification of this 

 theory was advanced by Parr (1932), who suggested that the luminous organ subserved the sexual 

 function of attracting the males (which have no functional illicium). This possibility has been further 

 discussed by Waterman (1948). 



Recently Bertelsen (1943) has been able to establish, beyond reasonable doubt, that the cephalic 

 tentacle, at least in C. holbolli, is pre-eminently a fishing lure. He showed that the arrangement and muscu- 

 lature of the basal bone was such that it could either be exserted or withdrawn, and continues (p. 194) : 

 ' When the tentacle is withdrawn, the prey attracted by the luminous bait on the exserted tentacle may 

 be lured straight into the mouth of the fish.' In connexion with this mechanism the dorsal tentacle is 

 important. This structure occurs in all Ceratiidae and has been variously described as a tentacle, ' papilla ' 

 or 'pore' lying immediately in front of the caruncles on the dorsal surface. Kroyer (1844) considered 

 it to be the second dorsal fin ray, and Regan & Trewavas (1932) described it as the third. Rauther 

 (1941)* dissected a damaged specimen of C. holbolli and believed that the tentacle contained the 

 prolongation of a pterygiophor which was jointed at its anterior end with the basal bone of the cephalic 

 tentacle. But Bertelsen, working on an undamaged specimen, showed that the dorsal tentacle is in fact 

 a sheath derived from the skin of the back, which receives the proximal part of the basal bone of the 

 illicium. From its insertion on the head this long, slender fishing rod continues in a trough along the 

 upper surface of the skull and between the dorsal muscles. When the rod is fully exserted the dorsal tentacle 

 is invaginated and appears only as a pore raised on a short peduncle. When the rod is withdrawn its 

 proximal end completely pierces the back and emerges, sheathed in pigmented skin, as this conspicuous 

 dorsal tentacle. Bertelsen thus established the identity of the ' tentacle ', ' papilla ' and ' pore ' of other 

 authors, and in the light of this evidence proceeded to revise the systematics of the Ceratiidae. 



Bertelsen does not say that he was able to move the rod in and out, since the discovery of its extra- 

 ordinary adjustability was deduced from morphological observations on fixed and hardened material. 

 Now I had not read his 1943 paper when I first examined the new specimen, without dissection, on 

 board the whaling factory ship ' Southern Harvester '. The following extract from my field notebook 

 * Quoted by Bertelsen (1943). Rauther's paper is not at present available in England (June 1949). 



