ZOOLOGY. 599 



Tbi« was first described hj the great American naturalist, Dr. Leidy, 

 and has recently been the subject of renewed examination by two other 

 naturalists of Philadelphia, Miss Sara G. Foulke and ]\Ir. Edw^ard Potts. 



The tentacular crown, or branchial organ, is considered by Miss 

 Foulke to be the feature of special interest. 



"Accordingto Dr. Leidy, the tentacles ])resentin an adult are eijjhteen 

 in number, besides two larger and longer tentacles situated midway 

 between the two lophophores. These larger tentacles are conspicuous 

 by their bright green color, and are, in fact, external continuations of 

 the blood- vessels extending lengthwise throughout the body. In shape 

 these tentacles taper from base to apex ; are convex on the outsiue, but 

 concave on the side which faces the center of the tentacular crown, so 

 that u transverse section would present the shape of a crescent. The 

 two edges thus formed are fringed with cilia, ^yhen closely watched, 

 the green tentacles are seen to i)ulsate with a rhythmical motion, con- 

 tracting and expanding longitudinally. The pulsation takes place in 

 each tentacle alternately. 



''At the moment of contraction the tentacle turns slightly on its axis, 

 outwards and towards the end of the lophophore on that side, at the 

 same time giving a backward jerk, returning to its former position at 

 the moment of exi)ansion. 



"By force of the contraction, the green blood filling the tentacle is 

 forced downward out of the tentacle, and flows along the blood-vessel 

 on that side of the body. On the expanding of the tentacle, the blood, 

 instantly returns and suffuses it, and thus the process goes on." 



Mr. Potts's observations were chiefly devoted to the manner in which 

 the woiMii takes its food. 



Although the crown of the tentacles imparts to the worms some re- 

 semblance toapolyzoan, " there is a noticeable difference in the effect pro- 

 duced by the motion of their cilia. In the latter a powerful incurrent 

 bears food i)articles, »S:c., towards the mouth as a vortex; in the former 

 case, while the motion draws these particles from without or behind the 

 circle towards the tentacles, the moment they pass between them they 

 are influenced by an excurrent bearing them forcibly away. This out- 

 flowing current is further shown by the fact that excrementitious mat- 

 ters are drawn rapidly forward through the tube, and ejected at its 

 anterior extremity. 



" As food, therefore, cannot be sucked into the mouth of the worm, we 

 find that it is carried in. Acceptable particles which touch the tentacles 

 are grasped by the cilia, and rapidly passed down among them in near 

 contact with the tentacle into grooves at the base of tlu^ above-men- 

 tioned i)rocesses, and thence into the digestive tract." 



Mr. Potts was also fortunate enough to be able to study the worm in 

 the act of buihling a tube. 



Ill its earliest stages, the tube "is a transi)ai'ent, smooth, and homo- 

 geneous slime-like excretion, within which the worm may be very clearly 



