PAIRING, COURTSHIP, AND PARENTAL CARE 315 



from the pouch is a much more difficult matter than in the 

 Pipe-fishes, and may occupy several hours, only fi\e or six 

 individuals being set free at a time. The small aperture of the 

 sac-like pouch makes it impossible for the young to return to 

 its shelter, and it is probable that they are retained for a longer 

 period than in the case of the Pipe-fishes. 



Finally, mention must be made of the Ceratioid Angler-fishes 

 (Ceratioidea), inhabitants of the mid- waters of the oceans, in 

 which the relationship between the sexes is unique among 

 fishes, and indeed among all vertebrates. The discovery of these 

 relations was made only two or three years ago, and provides 



^^^^^9lifti^®Si^i 



Fig. 114. 

 Photocorynus spiniceps : female with parasitic male, X i ^. (Male X 3.) 



one of the startling biological events of the present century. 

 All the large free-swimming individuals that have been captured 

 have proved to be females, and it has been shown that the 

 males are mere dwarfs and spend the greater part of their 

 lives as parasites upon the females. A fish taken near Iceland 

 was forty inches in length, and the attached male was about 

 four inches, the one, therefore, being one thousand times the [ 32 

 size of the other. Another female measured no more than 

 about two and a half inches, and had a tiny male, two-fifths of 

 an inch in length, attached to the top of her head above the 

 right eye (Fig. 114). This remarkable relationship seems to 

 have been evolved in relation to the habits and conditions of 

 life of the fishes. Living as they do in the comparati\e darkness 



