THE EGG. 



143 



albumen during its passage down the oviduct, and, in the ovi- 

 parous forms, a shell.* The shell is horny and generally oblong 

 in shape with the angles prolonged into four long coiled tendril - 

 like fibres (absent in the Skates), by which it is attached to 

 seaweed and other bodies. In Cestracion it is ovoid with a 

 spirally wound flange. In some viviparous Rays {Trygonorhina, 

 Rhinobatus) more than one ovum is enclosed in the same shell, 

 and the same fact has been observed in other forms. 



Many sharks and the Torpedoes and one or two other Raji 



'MP 



B 



Fig. 81. — A mile, B female uriuogenital organs of .'Jj/a 6a<is (from Wiedersheim, after T. J. 

 Parser), up abdominal pore; cl cloaca; epd convoluted anterior end of mesonephric duct 

 (vas deferera) of male lying on and concealing the epididymis ; fit anterior end of ovi- 

 duct ; fit' abdominal opening of the two oviducts ; ir interrenal organ (part of suprarenal 

 body) ; k metanephros ; mn.d mesonephric (longitudinal) duct of female ; od.g oviducal 

 gland ; oes oesophagus ; ov right ovary ; pn.d remains of oviduct in male ; ss sperm 

 sac, ««' its opening into the urinogenital sinus ; t left testis ; m6 dilated lower end 

 of mesonephric duct in the female ; ug.p urinogenital papilla in the male ; ug.s urino- 

 genital sinus ; u.p urinary papilla in female ; ur collecting tubes (ureters) of meta- 

 nephros, ut" their openings into the urinogenital (urinary) sinus ; ut dilated part of left 

 oviduct, ut' its opening into the cloaca ; vd lower end of mesonephric duct of male 

 (vas deferens) ; vs vesicula seminalis, vs' its opening into the sperm-sac. 



* The shell is formed round the ovum and its albumen in the lower 

 dilated part of the oviduct, but the material of which it is composed is 

 secreted by the oviducal gland. 



