302 ESTEBOPNEUSTA. 



Between these, brownish-green prominences are visible (the hepatic 

 appendages of the intestine), which, towards the posterior extremity 

 where the yellow glands disappear, are larger and more closely 

 aggregated. Finally there follows a distinctly ringed caudal region, 

 at the hind end of which is the anus. 



The contractile proboscis serves not only as a siphon to maintain 

 respiration, but also as a locomotory organ. It projects above the 

 level of the mud in which the animal is buried, and is said to take in 

 water by a terminal aperture (the existence of this opening has been 

 recently disputed) [and to pass it out into the mouth through a pore 

 at its base]. 



The mouth lies behind the anterior margin of the so-called collar, 

 and leads into a buccal cavity, the walls of which contain a great 

 number of unicellular mucous glands. The portion of the alimen- 

 tary canal which follows the buccal cavity bears the branchial frame- 

 work, and is divided into a dorsal and ventral part by two longitudinal 

 folds, so that it almost presents in transverse section the appearance 

 of a figure of 8. The intestine does not hang freely in the body 

 cavity, but, except in the region of the tail, is fastened to the body 

 wall by connective tissue; it is, however, always very closely attached 

 in the two median lines. Beneath the dorsal and ventral median 

 lines, where the two principal vascular trunks are visible through the 

 skin, two grooves, beset with strong cilia, run along the whole length 

 of the intestine. From these grooves secondary grooves are given off, 

 and as it were divide the whole surface of the intestine into islands. 

 Some distance behind the branchial region, on the upper side of the 

 intestine, the peculiar cell masses begin, which gradually assume the 

 form, of sac-like diverticula with ciliated internal walls. These 

 " hepatic appendages " are either disposed in a simple row along each 

 side (B. minutus Kow.), or densely aggregated together (Z>. clavigerus 

 Delle Ch.) 



The branchial basket-work which is placed at the commencement 

 of the alimentary canal projects on the anterior flattened part of the 

 body in the form of a ti-ansversely ringed longitudinal fold, and con- 

 tains a system of chitinous plates, which constitute its framework and 

 are connected in a peculiar manner by transverse rods. The water 

 taken in through the mouth passes through special openings in the 

 wall of the anterior portion of the alimentary canal into the ciliated 

 branchial spaces, to issue thence through the two rows of lateral 

 pores on the dorsal surface of the branchial region. 



The vascular system consists of two median longitudinal trunks, 



