(60) 

 reseiit the sectioned ends of a pair of lont;i tuainal muscle 

 tracts which are bilaterally placed, one on each side of the me- 

 dian dorsal line. (■p'ifc;.44) These two thick tracts of muscle 

 fibers extend posteriorly in the do rso-lat eral regions o -f Uio 

 Actinotrocha and do not disappear until the perianal rin^,- is 

 reached. They are very characteristic structures in Species, B., 

 (■*''i5S.44 to 4-r(h) ) but 1 iiavc not been able to make tr.em out 

 in Bpeci es , A. 



These muscle bands, no acuLt, servo to draw th^e anal end 

 0"^ the body o -^ the Actinotrocha up to ti.e oral end duriiij^ tiiO 

 metamorphosis. Tiiey are tne most hii-;,i;ly dovolopea muscle tracts 

 in the body of the Actinotrocha aiid their course is alraost iden- 

 ticsl ".vith ti-e course of the "dorsal nerves" tnat kasterman de- 

 scribes. 



Exarriinat ion of cross sectioi;s of Species, B. , in ti:e ro-zion 

 of tne vestibule shx)<vs the cut ends of numerous muscle fibors 

 v/i\ich are spread over the ventral surface cf t^.e collar. Passing^ 

 posteriorly, these fibers become massed into definite muscle 

 tracts, about half way oack from the vestibule to the ve-nt ral in- 

 sertion of collar- trunk mesentery. (Ti'i^s . 44( c) -44(d) ) Tnese 

 two ventraJ lon£:i tndinal tracts which are bilaterally placed 

 one on eacr. siae of the ventral median line become separated, in 

 most cases at lea-;t, from the vevitral body wall in trie rej_ion of 



