188 



BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



The atrial muscles in the young zooids are as shown in figure 147, 

 the condition evidently being one of immaturity. Over the future 

 atrial pore lies an enlarged blood sinus, and further atrial sphincters 

 will doubtless form in this region. There is a well-defined atrial 

 retractor muscle on 

 each side. There are 

 two circular basal 

 sphincters independ- 

 ent of the retractors, 

 and three delicate dis- 

 tal branches of the 

 retractors functioning 

 as sphincter muscles. 

 The retractor muscles 

 are continued into the 

 tip of the atrial si- 

 phon into the'] region overlaid by the blood sinus, where apparently 

 further sphincter fibers are to be formed. 



The gut is a compact "nucleus." The endostyle is asymmetrical, 

 its anterior end in a laeval zooid bending to the left, its posterior 

 end bending to the right. 



Thejeyes almost exactly resemble those of Apsteinia punctata, 

 as is shown by a comparison of figure 148 with figure 57 (p. 78). 



a.r 



a.r. 



Fig. 147.— Apsteinia asymmetrica, aggregated form. Dorsal 

 view of the atrial musculature of an immature zooid. 

 x 184 diameters. 



n. 



~f n T 



ig. 48.— Apsteinia asymmetrica, adult aggregated form; a sagittal section through the gan- 

 glion AND DORSAL EYE. X 345 DIAMETERS. 



Observe that the zone of origin of the nerves from the ganglion (n 

 in lig. 148 and zz in fig. 57, p. 78) is horizontal in A. asymmetrica and 

 inclined 45° in A. punctata, showing that in the latter species the 

 ganglion has rotated forward 40° more than it has in A. asymmetrica- 



