DE. T. DAVIDSON OX RECENT BRACHIOPODA. 31 



margin oi' the cirri, while the future position of the calcareous loop, or crura, was indi- 

 cated by a row of irregular-shaped spiculae. ... In these slightly advanced stages, the 



peduncle becomes much shoi'ter in proportion to the length of the sliell In aU these 



stages the peduncle has very slight adhesion to the rock or whatever substance it may be 

 attached to, in this respect differing greatly from the adult, which often requires at this 



age great force to detach it I was fortunate in observing an individual [slightly 



larger] in motion. The animal whirled quickly on its peduncle ; when at rest the sheUs 

 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 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 currents in the water. In this position, 

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

 for twenty or thirty seconds, and then, wdth an abrupt closing of the valves, suddenly 



assume its first position In watching these motions for a long time, one could not 



help being impressed with the fact that great 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 fm-ther caution was unnecessary." 



Prof. Morse then goes on to describe how in successive stages a fold on each side of 

 the stomach was first noticed, these folds being the first appearance of the liver, then the 

 upper portion of the digestive sac and that portion which answers to the CBSophagus and 

 stomach in the contracted state, while the lower portion is widely expanded. In a still 

 more advanced stage, he says : — " The shell is now becoming proportionally broader and the 

 cirri increase in number, though still forming a simple circle around the mouth. The 

 crura have also begun to form. At a considerably more advanced stage " The cirri are 

 more numerous, numbering thirty-one : two of them are seen encroaching upon the 

 circular lophophore, and at this stage the lophophore has begun to assume its hippo- 

 crej)ian character. 



" The crura are plainly seen supporting the crown of cirri, and the liver already shows 

 the first indications of its differentiations under the peculiar csecal ramifications which 



become so numerous in the adult The divaricators are completely formed, and 



between these two muscles is seen the lengthened intestine, the blind extremity of 

 which is held firmly to the shell by a membrane, called by Hancock the ventral 

 mesentery." At this stage " Radiating ribs, to the number of fifteen, ornament the 

 shell." 



Successive stages are then described. At p. 35 of his admirable memoir. Prof. Morse 

 enters into Ions: details in connexion with the structure of the shell ; he savs : — " In the 

 youngest stages of the shell the scale-like structure may be studied to the best advantage. 

 The scales are few in number, but slightly overlapping, and form a layer quite distinct 

 from the outer layer, which appears to be homogeneous, save the concentric lines of 

 gi'owth appearing like rows of oblong and flattened nodules. The terminal portions of 

 the pallial caeca within or upon this outer layer, are brown in colour and distinctly 



