60 MR. T. J. PARKER 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 Zygena, while the greater part of the first turn 
in Chimera is almost straight, so that the portion of the valve enclosed in the second 
compartment in that genus is, practically, 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, Pl. X.) with a section of 
the valve of Zygena (Pl. XI. fig. 10). These facts may be expressed in a tabular 
form, thus :— 
Type D. 
Type ¢. 
Type B. wi 
Type A. 
Spiral valve Scroll valve 
(Valvula spiralis). (Valvula voluta). 
/ 
y 
/ 
Typhlosole. 
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 D 
are derivable from the simple form A, and that, of the three, D is the most differen- 
tiated, in virtue of possessing the greatest extent of surface, and offering 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 Chimera, Cestracion, Notidanus, and Ceratodus, to Dr. 
Giinther for allowing me to examine specimens of Zygena and Carcharias in the British- 
Museum collection, and, chiefly, to Mr. Willis for devoting much time and trouble to 
the estimation of the surface in the chief forms of spiral valve. 
