VOL. 2, PT. 2.] 



APPENDIX. 



187 



I+1J 



organs seem to be fully formed, except that the atrial aperture 

 has not yet opened. The general structure, including the mus- 

 culature, will be described from these small zooids. 



In dorsal view (fig. 145Jl) one sees that the mouth and atrial 

 siphon are decidedly asymmetrical, right or left according to the 

 position of the zooid in the chain. The muscles in dorsal view 

 show some asymmetry, and in ventral view their asymmetry is seen 

 to be very great (fig. 1455). 



Musculature. — There are five body muscles. I and II are fused 

 over most of the dorsal surface. II, III, and IV are in contact, 

 or nearly so, in the region which corresponds apparently to the 

 mid-dorsal line. Muscles I-V,a are interrupted ventrally, their 

 ventral ends being very asymmetrically placed, as shown in figure 

 1455. Body muscle V is branched, as is usual with the last body mus- 

 cle. Its anterior branches, 

 V,a, are interrupted and &% z f- 3 



very asymmetrical ventrally. 

 The posterior branches, Y,b, 

 are continuous across the 

 ventral surface in front of 

 the intestinal nucleus. 



The oral muscles are best 

 seen in side view (fig. 146). 

 The intermediate muscles 

 are not alike on the two 

 sides. On the left side of a o.T. 



larval ZOoid this muscle Fig. 146.— Apsteinia asymmetrica, aggregated form. 

 11 , i i Oral musculature of an immature zooid, viewed 



arises below near the endo- FR0M THE LEFT SIPE . x m DIAMETERS . 

 style, running up and back, 



passing outside the oral retractor, and reaches the anterior edge of 

 body muscle I. On the right side it rises below well to the left 

 of the endostyle (fig. 145 A), and curves up to about the level of 

 the ganglion but does not reach body muscle I. The dorsal hori- 

 zontal muscle is present on each side, stretching from the third 

 sphincter of the upper lip to near the upper end of the inter- 

 mediate muscle. There is a well-developed oral retractor muscle 

 and three sphincters in each lip, the two sides being nearly alike. 

 The first sphincter in each lip is submarginal and delicate. The 

 second is wider, and the third is still broader. In dorsal view, 

 sphincters 2 and 3 of the upper lip seem almost to form one band, 

 but this is due to a foreshortened view of these muscles as they 

 lie on the inclined dorsal surface of the oral siphon. In side view 

 the true relations appear. 



