432 MEMOIRS OF THE AMERICAN ACADEMY. 



probably serves as a support or fulcrum for the slender base by which the proboscis is 

 attached to the collar. The shape of the proboscis is slightly different from that of 

 B. minutus, being pointed anteriorly and not truncated. 



Immediately behind the proboscis comes the collar, a part of the body somewhat 

 similar to the collar of Sabella, Clymene, and allied Annelids ; the anterior extremity 



I 



is deeply hollowed out, the edges projecting so as to conceal the slender connecting 

 stem of the base of the proboscis. The whole collar (as well as the proboscis, but in 

 a less degree) is filled with glands from which an immense quantity of white trans- 

 parent mucus is constantly and rapidly generated. The color of the collar is somewhat 

 darker than that of the proboscis ; it flares out both at the anterior and posterior ex- 

 tremity, and is slightly corrugated along the median dorsal part. The broadly open 

 mouth leads into what corresponds to the oesophagus of Tornaria. That part of 

 the oesophagus which is flanked by the gills is about twice as long as the proboscis, 

 the latter being from five to six times as long as the collar. 



Following the oesophagus we come to the convolutions of the former stomach, 

 which have taken an immense development, the intestine proper remaining very 

 much as it is in the younger stages, and occupying only a small portion of the pos- 

 terior extremity of the body. The alimentary canal is connected dorsally and 

 ventrally with the outer walls of the body along the median line, occupied by folds 

 which are strongly ciliated and send out small branches through the windings of 

 the alimentary canal, on each side of the large dorsal and ventral vessels, as described 

 by Kowalevsky, the branches of the two median vessels connecting them laterally. 

 Beyond the gills the alimentary canal is not as intimately connected with the walls 

 as in the anterior part. The alimentary canal becomes differentiated and forms 

 diverticula, — small, narrow folds which eventually connect with the main alimentary 

 canal only by a narrow slit ; these diverticula draw down the adjacent outer wall, 



forming a large number of small 



folds of a greenish color ; these 



folds, lined with whitish cells, give that part of the body a most peculiar appearance. 

 Kowalevsky calls these diverticula the liver. The limitation of -the liver organs is 

 not as well marked in the American Balanoglossus as Kowalevsky describes it in the 

 Mediterranean species, the folds become more and more distant towards the posterior 

 extremity, and extend far towards the anal end in the cylindrical portion of the termi- 

 nation of the body. Behind the liver the alimentary canal is simply formed of more 

 or less closely packed convolutions, and it becomes almost straight near the anal ex- 

 tremity. In Balanoglossus Kowalevskii, immediately behind the collar, along the 

 median dorsal line are situated the gills • they grow gradually smaUer towards the pos- 



