THE SHARK THAT HIBERNATES — MATTHEWS 419 



of 663 calories to give merely the energy required in swimming to col- 

 lect the food. Even if we multiply the recorded density of plankton 

 in the North Sea in November by three, the shark's intake could be 

 only 410 calories per hour under the most favorable conditions, and 

 it would be losing on the deal. So it solves its problem by throwing 

 away its rakers worn by a season's use, refraining from feeding, sink- 

 ing to the bottom and hibernating. At this moment there are probably 

 great schools of these enormous fish quietly resting on the bottom of 

 the sea, perhaps in the heads of the canyons at the edge of the conti- 

 nental shelf, with their metabolism running at its lowest level while 

 they grow their new gill rakers ready for browsing on next summer's 

 crop of planlrton. 



The "basking" of this shark is probably connected in some way 

 with its breeding as well as its feeding. The fish do not invariably 

 swim straight ahead ; sometimes two or more are seen to follow each 

 other about in comparatively small circles, apparently indulging in 

 elephantine gambols which may be a form of nuptial behavior. How- 

 ever that may be, it is certain that pairing takes place in the early 

 summer, though it may also take place at other times. As in all 

 elasmobranchs, or cartilaginous fishes, fertilization is internal, and 

 the sperm is transferred to the female by means of modified parts of 

 the male's pelvic fins called the claspers. Each clasper of the basking 

 shark is about 4 feet long, and its skeleton is rolled into a scroll that 

 forms a tube through which the sperm passes. The sperm is unlike 

 that of other fishes, for it is not a suspension of spermatozoa in a fluid 

 medium but is concentrated into spermatophores. The lower part of 

 the genital duct of the male is a large ampulla, a cavity of complicated 

 internal structure in which the sperm entering the fore end are gath- 

 ered into small masses around which a thick envelope of firm trans- 

 parent gristly substance is laid down. The core of each spermato- 

 phore into which the sj)erm are concentrated is about 1 cm. in diam- 

 eter, but the thickness of the envelope is such that the diameter of the 

 spermatophore is from 2 to 5 cm. About 5 or 6 gallons of these pecu- 

 liar bodies are tightly packed inside each ampulla, and float in a 

 watery fluid. 



The presence of great quantities of spermatophores inside the fe- 

 males in May showed that copulation was occurring then. Further- 

 more, the clasper of the male bears a movable spur armed with a hard 

 curved claw that evidently serves to maintain the clasper in position 

 within the common vagina of the female. Although many of the 

 females examined in May contained no spermatophores they carried 

 large internal lacerations made by the claws. The spermatophores 

 are received into a capacious uterus where a secretion acts upon them 

 and rapidly dissolves their hard envelopes, thus releasing the sper- 



