32 EARLY STAGES OF TEREBRATULINA. 



In figs. 8 and 9 are given side views of the shell at this period. The flatness of the 

 valves will be observed, again resembling Lingula in this respect ; the under valve is 

 much flatter than the upper one. I was fortunate in observing an individual at this age 

 in motion. The animal whirled quickly on its peduncle ; when at rest the shells were 

 always closed, and rested on the rock ; from this position it turned slowly more than half 

 way round, raising the body at the same time almost erect ; this movement being com- 

 pleted, 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 currents in the water. In this position, 

 with the valves widely open and eirri expanded, the animal would remain motionless for 

 twenty or thirty seconds, and then, with an abrupt closing of the valves, suddenly assume 

 its first position. These two positions are represented in fig. 10, where the animal is seen 

 from the side, and in fig. 11, where it is seen from above. The outline marked A repre- 

 sents the shells closed and at rest, while B represents the shells open ; the line of arrows 

 indicates the direction of the rotatory movement. 



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 ele- 

 vating and opening the shell, while the prompt closing of the valves, and the alert man- 

 ner in which the animal regained its first position seemed to show that food had been 

 secured, and further caution was unnecessary. 



In another stage, fig. 12, 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 independently of each other (fig. 14). 



In fig. 13 another view of the same individual is given, where the upper portion of the 

 digestive sac, or that portion which answers to the oesophagus and stomach, is in a con- 

 tracted state, while the lower portion is widely expanded. A peculiar constriction 

 appears at times between the two chambers of the digestive sac, which recalls the cardiac 

 or oesophageal valve, as seen in the Phylactolaematous Polyzoa ; it has no coniform projec- 

 tion into the stomach, and really appears more distinctly as an annular dilatation. All 

 traces of it disappeared 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 fig. 4, the cirri are shown, clothed with cilia ; in fig. 12 the cirri are shown plain, 

 while the cilia are shown lining the digestive sac. In fig. 15 only the calcareous spiculse 

 are shown ; but in all these cases each possesses the characters of the others, which for 

 clearness are shown singly. 



Fig. 17 exhibits the only example where the soft parts are drawn from an alcoholic 

 specimen. In this example is first seen a set of muscles, rendered visible by their con- 

 traction in alcohol, and consequent greater density. They are probably the divaricator 

 muscles, though somewhat in advance of what their position would be in the adult state. 



Owing to the contraction of the digestive sac, its diverticular cavities are sharply de- 

 fined, and the globular appearance of the lower cavity is marked. In another alcoholic 

 specimen of the same age, a band, evidently one of the lateral gastro-parietal bands, was 



