28 DISCOVERY REPORTS 



time in the surface current, and so move northwards towards the Antarctic Convergence, until forced 

 down in this region by either temperature or light barriers, or both, to continue north with the Antarctic 

 Intermediate Current under the conditions of tropical submergence. With further submergence in 

 a lower latitude this fish (or another generation) might find itself in the Warm Deep Current again and 

 so be returned to the Antarctic (Deacon, 1937, fig. 1). Or it may enter the northern circulation, since 

 Coe (1946) has suggested that there are areas, like the deep water off Bermuda (which has components 

 of Arctic, Antarctic and Mediterranean origins), where bathypelagic animals may collect in eddies or 

 be widely redistributed during the course of generations. 



Nothing can be said concerning breeding in relation to these hypothetical drifts of C. holbolli except 

 that reproduction is likely to take place in fairly deep water at a low latitude. This is suggested by the 

 regressed condition of the ovaries in the Antarctic specimen and by the fact that sixteen of the twenty 

 four known juveniles have been captured at stations within the tropics. 



PERCEPTION IN CERATIAS HOLBOLLI 



Waterman (1948) has described the Ceratioid Gigantactis longicirra as a floating, bathypelagic trap. 

 Even more so Ceratias holbolli deserves such a description, for the fishing lure in this animal, by its 

 extreme adjustability, achieves a mechanical specialization and efficiency unequalled among the 

 Ceratioidea. The very modifications of such a fish require that, if it is to survive at all, it must be 

 furnished with adequate sensory apparatus. It needs to apprehend the presence of prey and so entice 

 the latter into its mouth by retraction of the lure ; and it must be able to sense the approach of predators. 

 Yet the reduction of the senses of vision and olfaction, noticed by Waterman in Gigantactis, is carried 

 even further in Ceratias holbolli, where the adult female is functionally blind and the nostrils are 

 represented by vestigial tags. The problem, therefore, arises how the highly modified C. holbolli, 

 apparently helpless to escape, and defended only by its prickles, can have been able to evolve as a fish 

 blind when adult. Chun (1896) has indicated that luminous organs would betray their possessor to 

 predators in its vicinity. The Sperm whale, whilst seeking the squid which are its normal prey, was 

 presumably attracted in this way to the escal lamp of the Antarctic specimen. But it is conceivable that 

 an angler fish, being aware of the approach of predators, could evade them by extinguishing the tell- 

 tale light (Waterman, 1939^, 1948; Harvey, 1940, p. 161). 



The means of this perception in the adult C. holbolli is at present obscure. Whilst discussing the 

 attraction of males attention has been drawn to the evidence adduced by Brauer (1908) and Waterman 

 (1948) of a sensory function subserved by the esca in Gigantactis. But it was pointed out that in 

 Ceratias holbolli there are at most only two of those numerous filaments which characterize the esca 

 of Gigantactis and which might be supposed to be sensory in nature. We must probably look elsewhere 

 for the sensory apparatus in Ceratias holbolli. Now Waterman (1948) has shown by anatomical studies 

 that the stato-acoustic system of Gigantactis is considerably developed. Probably a similar or greater 

 development of this system is attained in Ceratias holbolli. Parker (1904) and Dykgraaf (1934) have 

 emphasized a ' lateral line sense ' supposed to make fishes aware of low-frequency movements in the 

 water, so it may be that the lateral line organs on the head of C. holbolli are sensitive to local disturbances 

 and that these are mediated with especial sensitivity.* By the amplitude of these disturbances the fish 

 may be informed of the vicinity of greater or lesser animals, of predator or prey. 



Of course this is supposition, but at least it may serve with whatever else is tentative in the present 

 account to draw attention to the biological problems raised by only one, albeit the most specialized one, 

 among this curious group of bathypelagic angler fishes. 



* Similarly the blind group of amblyopsid Cyprinodonts show on the head and body a special development of 

 papillae, believed to subserve perception (Norman, 1931). 



