122 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Cat. No. 6585, U.S.N.M. (test of solitary form) , Albatross station D. 

 5244, Pujada Bay and vicinity, Philippine Islands; May 15, 1908; 

 surface; surface temperature, 85° F. ; surface density, 1.02497; 

 3 specimens. 



Cat. No. 6609, U.S.N.M. (solitary form. Tests) , Albatross station 

 D. 5241, Pujada Bay and vicinity, Philippine Islands; May 14, 1908; 

 surface; surface temperature, 85° F. ; surface density, 1.02453; 10 

 specimens. 



Cat. No. 6610, U.S.N.M. (aggregated form), Albatross station D. 

 5243, Pujada Bay and vicinity, Philippine Islands; May 15, 1908; 

 surface; surface temperature, 84-85° F. ; surface density, 1.02453; 

 one specimen. 



THETYS VAGINA, solitary form. 



Like some of the Ritterias, the solitary form of this species has a 

 variable number of body muscles (fig. 114). The number is about 

 the same as in Ritteria jricteti. 16 to 20, or more. All the muscles 

 are interrupted on the dorsal mid line, and many of the anterior 



Fig. 114.— Thetys vagina, solitary form, viewed from the right side, one-half natural size. 

 Modified from Ritter (1900). 



and some of the posterior ones are also interrupted dorso-laterally. 

 The muscles barely extend onto the ventral hall of the bodj r . 



The intermediate muscle (fig. 115) is reduced to a mere vestige at 

 the angle of the mouth. 



The oral muscles are rather weakly developed for such a huge salpa. 

 In two specimens I have had for study the conditions arc somewhat 

 different. The relations in the smaller individual are shown in 

 figure 114. Those in the larger individual appear in figure 115. In 

 the first figure the inverted portion of the lower lip is drawn forward 

 to the outer surface. In the second figure the natural relations are 

 shown. Two oral retractor muscles are present, each continued for- 

 ward into a well-developed sphincter of the lower lip (Z. 2 and 3). 

 In the smaller specimen (fig. 114) these are distinct; in the larger 

 specimen (fig. 115) they are united through the ventral half of their 

 course. Another very delicate sphincter (I. 4) is present in both 

 individuals. In the smaller specimen (fig. 114) it is continuous at 

 its upper end with the ventral edge of the ventral oral retractor and 



