1901.] NATURAL SCIENCES OF PHILADELPHIA. 669 



first intestinal pouches — the circular muscles of the esophagus 

 increase so greatly in number that they form a most conspicuous 

 layer. In the region of its maximum development this layer 

 becomes nearly half as thick as the circular layer of the body walls in 

 the same section. In no other species of the Lineidse has this 

 muscle been found of even approximately this thickness. Its fibers 

 connect in part with the circular layer of the body walls and to a 

 lesser degree with the circular muscles of the proboscis sheath. 

 But few fibers lie on the dorsal wall of the esophagus, so that this 

 organ is largely bound up with the proboscis sheath in a continu- 

 ous layer of muscles, and one cannot fail to see the striking resem- 

 blance between this circular layer and the inner circular muscles 

 that are so highly developed in precisely the same region in 

 Carmoma." 



Since, as Dr. Coe says, the I'esemblance between this mus- 

 cular layer and the inner circular layer of Cariiioma is so striking, 

 why should we not regard them as one and the same structure, that 

 is, as homologous ? In what particulars do they differ ? 



Biirger (1895), p. 234, gives the following definition for the 

 inner circular muscle layer of the Protonemerteans and Carinoma. 

 *' Die Leibesmusculatur. Zu dieser recline ich einen aus Riugfibril- 

 len zusammengesetzten Muskelschlauch, welcher bei den Protone. 

 mertinen, vor allem bei Cariaina grata, und Carinella polymorpha, 

 superha und linearis, und unter den Mesonemertinen bei Carinoma 

 armandi um Vorderdarm und Rhynchocolom entwickelt ist, diese 

 beiden Hohlcylinder einschliessend. Diesen Muskelschlauch nenne 

 ich die inuere Ringmuskelschicht." Biirger also states that the 

 fibres of the inner circular muscle differ in no way from those of 

 the body wall. 



Biirger further speaks, p. 235, of the crossing of fibres that 

 frequently occurs in the dorsal and ventral median line of the 

 body, between the inner circular and the outer circular layer of 

 the body wall. " Eine sehr merkwiirdige Erscheinung wird 

 dadurch hervorgerufen, dass die innere Kingmuskelschicht in 

 Beziehung zur iiusseren Ringmuskelschicht, also der Ringmuskel- 

 schicht des Hautmuskelschlauchs tritt. Das geschieht, indem 

 dorsal und ventral in der Medianebene des Thierkorpers von links 

 und rechts Muskelfasern aus dem Verbande beider Ringmuskel- 

 schichten heraustreteu, und, die Liingsmuskelschicht des Haut- 



