60 



ME. T. J. PAEKEE ON THE INTESTINAL 



the first quarter-turn of the attached edge in Raia is hardly more curved than the 

 homologous portion of the valve of Zygcena, while the greater part of the first turn 

 in CMmcem is almost straight, so that the portion of the valve enclosed in the second 

 compartment in that genus is, practicaUy, a scroll valve. The same may be said of the 

 portion contained in the first compartment (the bursa) in Raia, as will be seen by 

 comparing a transverse section of that part of the gut (fig. 3, PI. X.) with a section of 

 the valve of Zygcena (PI. XI. fig. 10). These facts may be expressed in a tabular 

 form, thus : — 



Type D. 



Tj-peC. 



Type B. 



Type A. 



Spiral valve Scroll valve 



(Valvula spiralis). (Valvula voluta). 



Ti/phlosole. 



This Table is intended to express that both spiral and scroll valves are derivable 

 from the typhlosole, that the then culminating forms of the spiral valve B, C, and JD 

 are derivable from the simple form A, and that, of the three, 1) is the most differen- 

 tiated, in virtue of possessing the greatest extent of surface, and oflFering the greatest 

 resistance to the passage of the intestinal contents. 



§ 22. In conclusion, I have to express my thanks to Professor Huxley for placing 

 at my disposal specimens of Chimwra, C'estracion, Notidanus, and Ceratodus, to Dr. 

 Giinther for allowing me to examine specimens of Zygcena and Carcharias in the British- 

 Museum collection, and, chiefly, to Mr. WiUis for devoting much time and trouble to 

 the estimation of the surface in the chief forms of spiral valve. 



