Fishes of the Western Nortli Atla7ttic 141 



nerves as in the Electric Rays. Their embryonic derivation is from the caudolateral 

 musculature.''' 



In one set of observations, shocks of about one-half volt were recorded instrumen- 

 tally per centimeter of length of organ. ^" But we find no recorded instance of a fisher- 

 man reporting a shock from any Skates of this genus, though many thousands of them 

 are handled yearly; nor have we ever felt the least sensation from grasping the tail of 

 a Skate other than the rather unpleasant one of being wounded by the thorns. 



Sixe. The various species of the genus Raja of the western North Atlantic range 

 in length from about iVa to about 5 feet, perhaps to as much as 6 feet, and in weight 

 from about a pound to perhaps 50-60 pounds (p. 223). The females, at least in most 

 cases, are larger than the males, often by as much as one-third. 



Developmental Stages. In the commercial catches in British waters the females 

 considerably outnumber the males. This disparity appears to result from the fact that 

 the two sexes are more or less segregated, the gravid females apparently congregating 

 In more compact bodies or schools than the males. ^^ 



Skates are described as mating ventral side to ventral side, and pairs so engaged 

 are sometimes hauled up on hook and line. It has been observed*^ that the males and 

 females of one of the larger European species {R. batis) hold their discs flat while mat- 

 ing; but the female of the smaller R. asterias curves her pectorals ventrally, while the 

 male, rolling the outer corners of his pectorals out of the way ventrally, then bends the 

 fins inward around her back, which brings his alar spines in position to fasten to her. 



At least for some of the larger species it is reported that only one clasper is intro- 

 duced into the cloaca of the female at a time, but for other species it is said that both 

 are introduced simultaneously.'* 



Just after copulation the claspers are much swollen and reddened by suffused 

 blood.34 



Experiments*^ have proved that the egg is fertilized just before its capsule is formed 

 around it. The process by which the sperm is introduced into the oviduct has not 

 been traced for any Skate or Ray, but according to Clark the female apparently can 

 lay a series of eggs fertilized by sperm from one act of coition. Completion of the egg 

 capsules and extrusion of the egg appears to follow shortly after fertilization. 



Egg capsules of Skates are horny or leathery in texture, ranging in color from 

 light auburn to dark brown or even black. The shell, composed of a substance resem- 



29. For a detailed account of the electric elements and their development in various Skates, see especially Ewart (Philos. 

 Trans., [B] J79, 1888: 399-416, pis. 66-68; 1889: 539-552, pis. 79-80). 



30. See Sanderson and Gotch (J. Physiol., 9, 1888 : 141) for a detailed account of these experiments and of the general 

 nature of the electric discharges. 



31. For summary of available evidence on this point, see Steven (J. Mar. biol. Ass. U. K., iS, 1933: 611). 



32. See Le Danois (Vie et Moeurs Poiss., Payot, Paris, 1949: 199, text figs. 55, 56) for an eye-witness account and 

 illustrations of mating pairs of Raja batis and of R. asterias. 



33. Fowler (Rep. N. J. Mus. [1905], 1906: 730) quotes an eye-witness account of a pair of Raja eglanteria harpooned 

 while in the act of coition, the male with both claspers inserted. 



34. See Leigh-Sharpe (J. Morph., j6, 1922: 242, fig. 10) for illustration of clasper of Raja blanda, relaxed and distended. 



35. Clark, J. Mar. biol. Ass. U.K., 12, 1922: 584. 



