418 Dr. E. S. Morse on the Early Stages 



the upper one. I was fortunate in observing an individual 

 at this age in motion. The animal whirled quickly on its 

 peduncle ; Avhen at rest the shells were always closed, and 

 rested on the rock ; from this position it turned slowly more 

 than halfway round, raising the body at the same time almost 

 erect ; this movement being completed, the valves would very 

 slowly open, and the cirri expand as if to perform a grasping 

 motion ; in no case, however, were they projected beyond the 

 margin of the valves. The cilia lining the cirri produced 

 gentle cun-ents in the water. In this position, with the valves 

 widely open and cirri expanded, the animal would remain 

 motionless for twenty or thirty seconds, and then, with an 

 abrupt closing of the valves, suddenly assume its first posi- 

 tion. These two positions are represented in fig. 5, where 

 the animal is seen from the side, and in fig. 6, where it 

 is seen from above. The outline marked A represents the 

 shells closed and at rest, Avhile B represents the shells open. 



In watching these motions for a long time, one could not 

 help being impressed with the fact that caution was evidently 

 indicated in the slow and careful movements made in elevating 

 and opening the shell, while the prompt closing of the valves, 

 and the alert manner in which the animal regained its first 

 position, seemed to show that food had been secured and fur- 

 ther caution was unnecessary. 



In another stage (fig. 7) the tentacles were seen of various 

 lengths, some of them just budding from the lophophore. A 

 fold upon each side of the stomach was first noticed ; these 

 folds are the first appearance of the liver. At this time the 

 hepatic folds expand and contract inde]iendently of each other. 



In anotlier view of the same individual the ujiper por- 

 tion of the digestive sac, or that portion which answers to 

 the oesophagus and stomach, was in a contracted state, while 

 the lower portion was widely expanded. A peculiar constric- 

 tion appears at times between the two chambers of the 

 digestive sac, which recalls the cardiac or oesophageal valve 

 as seen in the PhylactolaMuatous Polyzoa ; it has no coni- 

 form ])rojeetion into the stomach, and really appears more 

 distinctly as an annular dilatation. All traces of it dis- 

 ajipcarecl during certain expansions and contractions of the 

 gastric walls. All portions of the sac and the lateral folds 

 were strongly ciliated ; and the food, now gathered into round 

 pellets and again scattered in granules, was violently impelled 

 back and forth. 



In an alcoholic specimen there was first seen a set of 

 muscles, rendered visible by their contraction in alcohol and 



