<>/' Tcrebratulina scjiti-ntrioiiali.s. 410 



consequent p^reatcr density. They wore |)r<il)ably the ilivari- 

 cator nmsck's, though soinewliat in advance ot" what their 

 position wouUl be in the aduU state. 



Owing to the contraction of the dif^estive sac, its diverticular 

 cavities were sharply defined, and the globular a])])earance of 

 the lower cavity was marked. In another alcoholic s[)ecinien 

 of the same a,<;e, a band, evidently one of the lateral gastro- 

 parietal bands, was made out. As this could not be verilicd 

 m other specimens of the same a<:;e, the figure is not given. 



A still more advanced stage is shown in fig. 12. The shell 

 is now becoming proportionally broader ; and the cirri in- 

 crease in number, though still forming a simj)le circle annind 

 the mouth. The crura have also begun to form. 



In fig. 13 a considerablv more advanced state is shown. 

 The valves have been forcibly separated, and the smaller one 

 is thrown back. The cirri are more numerous, numbering 

 thirty-one ; two of them are seen encroaching upon the cir- 

 cular lophophore ; and at this stage the lophophore has begun 

 to assume its hippocrepidan character. 



The crura (cr) are {daiuly seen supporting the crown of 

 cirri ; and the liver already sliows the first indications of its 

 difl:erentiation into the peculiar caical ramifications which 

 become so numerous in the adult ; and at this stage is seen 

 the division of each lateral portion of the liver into a dorsal 

 and a ventral lobe. The liver is divided into a series of caeca, 

 though these are united. 



The divaricators (d) are completely formed ; and between 

 these two muscles is seen the lengthened intestine, the 

 blind extremity of wdiich is held firmly to the shell by a 

 membrane, called by Hancock the ventral mesentery. 



The ap|)earance of the shell at this stage is represented in 

 fig. 16. lladiating ribs, to the number of fifteen, ornament 

 the shell. It will be seen by this figure that the seta3 corre- 

 spond in growth and position to the radiating furrows ; and 

 this observation is also made by Hancock in his examination 

 of the adult. A well-defined concentric line seems to indicate 

 the earlier Liiif/ula-shaiied shell ; and though no ribs appear in 

 the earlier stages, they are defined upon this area afterwards ; 

 and it would appear from this that the ribs are formed on the 

 inner surface, and that the seta3 direct and induce the furrow. 

 The lobes of the liver (I) and the peduncle (p) and peduncular 

 capsule are shown in this figure. 



In fig. 14 a stage still more advanced is given ; the valves 

 are thrown back, disclosing the stomach and intestine sus- 

 pended from the calcareous loop. The crura {cr) are well 

 defined ; and the ventral mesentery (v m) is more distinctly 



