672 PROCEEDINGS OF THE ACADEMY OF [DcC. , 



with an enormous thickening just in front of the middle intestine; 

 E, shows the condition in Zygeupolia and Micrura. In the last two 

 forms the inner circular layer is absent from the entire oesophageal 

 I'egion, and is represented merely by the thickened part in front of 

 the middle intestine, and a short, thin, anterior extension of this." 



In this connection it is interesting to note that in Cephalothrix 

 aliena, a new species from the Maldive Islands recently described 

 by Punnett (1901 a), a very delicate inner circular muscle layer is 

 present in the oesophageal region. 



From the facts just enumerated it is evident that the inner cir- 

 cular muscle of the Heteronemerteans may be regarded as the rem- 

 nant of a layer once continuous throughout the body. 



The accompanying table shows the comparative extent of the 

 inner circular muscle layer in the different genera in which it 

 occurs. 



The second part, relating to the muscular crosses between inner 

 and outer circular layers, shows that there is great variation in 

 this respect in the genus Cavinella. 



^ The facts in regard to the .distribution and structure of the inner circu- 

 lar muscle in the genus Carinella have been obtained from Burger's mono- 

 graph. 



