184 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



(fig. 49, p. 72) and the Cyclosalpas (pi. 1, fig. 1; pi. 3, fig. 9; pi. 7, 

 fig. 19; pi. 11, fig. 26), we might assign eight or perhaps nine to 

 the body muscle series, preferably nine. In any case the two species 

 closely agree in musculature, body muscle IX (or the basal cloacal 

 muscle, if one prefers so to name it) being the same in the two, 

 showing the same abortive anterior branch below and the same well 

 developed posterior branch passing around the body between the 

 cloacal siphon and the gut evagination. 



The intermediate muscle is large and the horizontal muscle well 

 developed. <There are five oral sphincters in each lip. The first and 



o.n 



Fig. 141.— Apsteinia asymmetrica, embryo. A dorsolateral view of the atrial siphon and the 



ADJACENT PARTS. X 102 DIAMETERS. 



second sphincters of the lower lip lie upon the incurved portion of 

 the lip. Posteriorly they unite to form the dorsal oral retractor 

 muscle, which is continuous with them alone. As in Apsteinia 

 punctata (figs. 49, p. 72; and 50), the posterior end of the dorsal 

 oral retractor abuts upon the front edge of the first body muscle. 

 Also the ventral oral retractor divides posteriorly into dorsal and 

 ventral branches, the dorsal one of which runs back as far as the 

 eighth body muscle, the ventral branch being shorter. In A. asym- 

 metrica it reaches to the middle of the fifth body muscle, being a 

 little longer than in A. punctata. The ventral oral retractor muscle 

 divides anteriorly to form muscle 5 of the lower lip and muscle 4 



