Fishes of the Western North Atlantic 67 



On the one hand the Whale Shark {Rhincodon) reaches a length of at least 45 and prob- 

 ably 50 to 60 feet, making it by far the largest of fishes, while certain scyliorhinids (p. 

 213) and triakids (p. 239) mature at lengths of only 300 to 400 mm. (less than 1V2 

 feet). 



Breeding and Development. Fertilization is internal (p. 62). The males have a 

 pair of copulatory organs (claspers or myxopterygia) that are developed as appendages 

 from the inner edges of the pelvic fins, supported by cartilages derived from the basiptery- 

 gial cartilage of the latter, with a groove along the inner side for the guidance of the sperm. 

 In copulation they are inserted through the cloaca of the female into her two sexual ori- 

 fices.* In some species at least, as in the European Scyliorhinus caniculus, only one clasper 

 is inserted at a time and coitus lasts about twenty minutes. As a rule the eggs are enclosed 

 in horny cases, at least for a time, but the Greenland Shark (Somniosus) may be an excep- 

 tion (p. 520). 



Development is oviparous in some sharks, ovoviviparous in the majority and truly 

 viviparous in still others. In the first type the horny egg capsules usually (but not always) 

 bear long tendrils at the corners at one or both ends, by which they are attached to algae, 

 etc.} in one group (Heterodontidae) there is also a very prominent spiral flange, giving 

 the egg a very distinctive appearance. In one species representing this category {Scylio- 

 rhinus caniculus) the period of incubation is 157-178 days.' Among the ovoviviparous 

 species the embryos, early liberated from the capsule, develop in the oviduct of the 

 mother; they are nourished from the original yolk alone which is chiefly in the yolk sac, 

 or from yolk, as well as from nutritive fluids secreted by filaments which are developed 

 from the walls of the maternal oviducts; these nutrients are absorbed both by the yolk 

 sac of the embryo and in many cases by appendages borne by its stalk, the so-called um- 

 bilical or placental cord. The young are not born until fully formed and after the yolk sac 

 has been absorbed. In the viviparous species the young lie in special uterine dilations of 

 the oviducts during development; the yolk sac develops folds and processes that inter- 

 digitate with corresponding folds of the uterine wall, thus forming the so-called yolk- 

 sac placenta. The number of young is small, as compared with many bony fishes; the 

 maximum number so far reported in a gravid female of any ovoviviparous shark of which 

 we have found record is 82. 



Intelligence and Senses. It is recognized by common observation that the intelligence 

 of sharks is of a very low order, alth'ough we cannot find that any significant tests have 

 been made of their capacity for learning. Their indifference to injury of any kind is pro- 

 verbial. In numerous recorded instances a shark, severely mutilated or even disembow- 



also instructive, since in this case entire series are involved and not merely individual teeth alone; Spiny Dogfish 

 are so commonly stocked by biological supply houses that large numbers are easily to be had. 



6. The method of copulation with which Aristotle was acquainted and which is now a matter of common knowledge, 

 was rediscovered by Louis Agassiz (Proc. Boston Soc. nat. Hist., i^, 1871 : 340) ; see also Garman and Putnam 

 (Proc. Amer. Ass. Adv. Sci., ij [2], 1874: 14) and Garman (Proc. Boston Soc. nat. Hist., ly, 1875: 171, 172). 

 For an eyewitness account of the act of coition in Scyliorhinus caniculus, see Bolaw (Z. Morph. Okol. Ticre, ^5, 

 1888: 321) i and Liibbert and Ehrenbaum (Handb. Seefisch. Nordeurop., j, 1936: pi. 20, fig. 249) show an ex- 

 cellent photograph of a pair so engaged. 



7. Observations in the Hamburg Aquarium; see Bolaw (Z. Morph. Okol. Tiere, 35, 1888: 324). 



