No. 4,S5] 



THE FUNCTIONS OF THE SPIRACLE 



289 



structure is present, so that water may pass either way. Dumeril 

 ('65-70, tome 1, p. 210) states that water usually enters the mouth 

 through the spiracle, but less frefjuently passes in the reverse 

 direction. 



While at rest on the bottom of an a<|iiai-iinii, the >katc sli^iitly 

 elevates the head above the surface of tlic I.oKom in tli(> maiiner 

 described in Brehm's Thierleben (Breiini, 7!), ]>. .isD. wliicli may 

 well be quoted : "Abweichend von andercii HocU'niisclu'ii lie^jen 

 sie mit dem Vordertheile ihres Leibes niemals fc.st aiif. sondern 

 stiitzen sich so auf ihre Brustflossen, dass in dcr Mitte ciii I lolilraum 



mit Wasscr zu versoro-en. offnen sie ihre AtluMul.K h.^r. indcni sie 

 dcii Xolhen zuriickziehcn, fallen die Kiemensackr. M-hlies.eu die 

 Athemlocher und treiben das verbrauehte Wasser .luicli die 

 Kiemenspalten nach aussen." Acconiinii- to my observations the 

 skate takes in water not only by the spiracle but also tliroui^li the 

 mouth, although considerably more water ent(>rs through the 

 spiracle than through the mouth. 



When fully open the external aperture of the spiracle in the 

 common skate is nearly elliptical in outline, but the curvature of 

 its anterior margin is much greater than tiiat of its posterior margin. 

 The anterior lip of the opening bears tiie rmhinentary gill and 

 the closing of the spiracle is effected mainly i)y the contraction of 

 this gilled lip, while the posterior lip, being nearly straight when 

 relaxed, contracts but little. 



pendidiun-like regularity. Dm'ing one of the prolonged resting 

 periods of llu^ fish, the interval between successive openings is 

 longer than when the fish is active, and the spiraclt' is not opened 

 wide,— indcvd. the o])ening may be only a narrow slit. During 

 more active rt\s[)iration the anterior lip of the spiracle moves back 

 ami forth with a (piick .lecisive motion an.l the spiracle is opened 

 to its ittmost width. .Vs the spiracular valve opens, the l.rancliial 



tightly closed. At the same iini(> that the spiracle is open, the 

 moiuh also is opened more or less and a certain (piantity of water 

 enters. I satisfied myself as to the inward current at the mouth 



