132 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



IM 



adult, with both first and second dorsal sphincters. There are two 

 complete dorsal sphincters and two incomplete, the fourth much 

 reduced in the adult. There are two ventral sphincters, the second 



being double along the 

 middle portion in the 

 embryo. In the adult 

 the posterior division 

 of the second ventral 

 sphincter separates 

 and lies independent 

 behind the main trunk 

 of the sphincter. 

 There is a weakly de- 

 veloped group of lon- 

 gitudinal fibers at the 

 mid-ventral line, run- 

 ning back from the 

 posterior division of 



Fiq. 120.— Pegea confederata, solitary FORM, ORAL MUSCULA- ,i i , , 



TURE OF THE RIGHT SIDE VIEWED FROM WITHIN. MODIFIED FROM "D.& SCCOnQ VCntral 



Strieff (1908). The oral musculature of the aggregated sphincter. Across the 



ZOOID IS SIMILAR. tip pi 



dorsal surface of the 

 base of the atrial siphon there runs a well-developed muscle band 

 (fig. 119, A). This connects on each side with a band which runs 

 forward and toward the median line, reaching about halfway to 



Fig. 121.— Pegea confederata, embryo, atrial musculature in ventral view. The atrial siphon 

 was cut open along the dorsal mid line and the flaps laid out laterally. x 150 diameters. 



body muscle IV. These basal atrial muscles of the dorsal surface 

 are not represented in figures 121 and 122. Across the ventral 

 surface of the base of the siphon there is a well-developed muscle- 

 band (figs. 119, B, 121, 122), a small branch from which on each side 



