336 Memoir Sears Foundation for Marine Research 



genera of the family. It has been described as renewed yearly, but we find no definite 

 evidence that its replacement follows any regular periodic schedule, nor does this seem 

 likely to us. While the majority of specimens are armed with a single spine, others have 

 two, rarely three or even four, showing that new spines may develop before the old 

 one is dropped. On the other hand, it is not unusual to find specimens with tails from 

 which the spine has been dropped (leaving only a scar) before any trace is to be seen 

 of the spine that should succeed it. At least in some species the replacement spine 

 may develop either close anterior to the pre-existing one or close posterior to it.^ How- 

 ever, in other species it may be that the replacement spine invariably develops either 

 anterior to the older one (Figs. 83 and 90, Dasyalis centroura and Z). say) or posterior 

 to it (Dasyatis sabina. Fig. 88). 



The upper (anterior) surface of the spine varies from low-half-oval to nearly semi- 

 circular in cross section; its lower (posterior) surface has a rounded median ridge 

 flanked on either hand by a deep furrow extending nearly to the tip; the rows of mar- 

 ginal teeth mark the transition from upper surface to lower. Although the spine itself 

 Is not mobile, the tail is so flexible that it swings far away from the terminal part of 

 the spine when lashed about, thus bringing the spine into a position favorable for 

 penetrating whatever It may strike. The tails of large specimens are so powerful that 

 It Is not exceptional for their spines to drive through a heavy boot and several layers 

 of clothing, to penetrate full length into an arm or leg, or to pierce the side of a wooden 

 boat deeply. Comparative anatomists and ichthyologists of the twentieth century 

 commonly regarded the effects of Sting Ray wounds (p. 333) as due to mechanical 

 Injury and to infection by the mucus of the Ray's skin rather than to any specific 

 poison. But as long ago as 1848^ it was pointed out that the symptoms following 

 these wounds are similar to those resulting from bites by poisonous snakes. It seems 

 well established now that the spines do secrete a poison from cells lying In the lateral 

 grooves along the side that faces the tail.' While the evidence to this effect is circum- 

 stantial, the pain and swelling follow far sooner after the wound is inflicted than might 

 be expected In the case of an ordinary Infection. The effects resemble so closely the 

 effects of wounds by the European Weaver Fishes, Trachinus (proved venomous by 

 clinical experiments of various kinds), and the secretory organ of the Sting Ray resem- 

 bles that of Trachinus so closely In histological structure, as to leave no reasonable 

 doubt of the venomous nature of the spine.* And the final proof has recently come 

 from laboratory experiments on the properties of their venom ^ and on the effects of 



5. In Dasyatis imbricala (Bloch and Schneider) iSoi from the East Indies, the replacement spine is posterior in two 

 out of 17 double-spined specimens that we have examined, anterior in the others. 



6. By R. Schomburgk; see p. 339, footnote 24. 



7. See Evans (Philos. Trans., [B] 212, 1923: 1-33) for the histology of the spine organ, Jorg (Nuov. Reun. See. Ar- 

 gent. Patol. Reg., 1939: 1599-1616) for the closely allied Potamotrygonidae, and Evans (Sting Fish and Sea Farer, 

 1943) for a popular account of venomous fishes. 



8. For an extended historical account of the effects of Sting Ray wounds, see Gudger (Bull. Hist. Med., 14, 1944: 

 467-504). 



9. Vellard (C. R. Acad. Sci. Paris, 792, 1931: 1279; Mem. Soc. zool. Fr., 29, 1932: 514-532); see also full summary 

 and discussion by Gudger (Amer. Nat., 81, 1947: 297). We might point out also that Jorg (Nuov. Reun. Argent. 

 Patol. Reg., J, 1939: 1603), who arrived at a contrary conclusion for Potamotrygon, did not study the histology 



