426 On the, Early Stages o/" Tercbratulina septentrionalis. 



reoua spicula ; ai, notch for pallial cteca ; h, liaimal valve ; N, neural 

 valve. 



Plate XV. 



Fir/. 1. A few egg-.s in their natural position, from the pallial membrane 



of an aclult individual. 

 Fi(j. 2. Earliest stage noticed. This was attached to rock, resting upon 



the broad hinge-margin. 

 Fiij. ?y. Another stage, in which the body has rapidly lengthened, and 



the peduncle is equal in length to the remaining portion of the 



animal. 

 Fiy. 4. Stage in which a few cirri are developed, with the cesophagus 



and stomach hanging below. 

 Fiy. 5. Tlift animal at rest and in action. 

 Fiy. G. The same, from above, reversed. 

 Fiy. 7. A more advanced state, \vith the liver as a simple hepatic fold on 



each side of tlie stomach. 

 Fiy. 8. Portions of two cirri, highly magnified, to show more plainly the 



form of the spicula. 

 Fiy. 9. A portion of the hiemal valve. 

 Fiy. 10. A portion of the neural valve. 

 Fiy. 11. The same portions before separation. 



Fiy. 12. A slightly more advanced stage, showing the crown of cirri. 

 Fig. 1.3. A still more advanced stage, with the ha-mal valve forcibly 



thrown open, showing the divaricator muscles with the stomach 



between them. The crown of cirri shows the first indications 



of its bilobed character. 

 Fiy. 14. A stage more advanced ; valves forcibly opened, showing all the 



parts plainly. 

 Fig. 14 a. A highly magnified view of the stomach, hepatic folds, lateral 



bands, &c. of tig. 14. This figure shows a focal ma.-is rolled in 



a spiral form, in the act of being discharged through the mouth. 



The line bordering the upper portion of the figure indicates the 



inferior margin of the crural processes. 

 Fiy. 15. The h.nemal valve, vnth the crown of cirri &c. 

 Fig. 16. A view of fig. l."> with the valves closed. 



Plate XVI. 



Fiy. 17. A stage considerably more advanced than the preceding ones, 



showing the lophophore already bilobed, but with the cim not 



deilected. (,';ecal lobes of the liver few, but separated. 

 Fiy. 18. Showing the lophophore with the cirri deilected. 

 Fiy. v.). The arms of the lophophore more sharply bt'ut ; the central 



processes first indicated. The hiijhlv fiexible lip is here seen in 



folds. 

 Fiy. 20. A stage slightly more advanced than the preceding. The lip is 



seen thrown back, disclosing the capacious mouth. 

 Fiy. 21. A stage more advanced, in wliich tlu' lophophore begins to 



assume the characters of the adult. The ciiTi are now more 



nunu'rous and more attenuated, and the lip is not so widely 



refiected. 

 Fiy. 22. View of tlie mouth of an adult individual, showing the oral 



tubercle and oral groove. 

 Fiy. 2.'J. Fragnu^nt of shell, highly magnified, showing scales, tubules, 



and outer layer, v.itli lir.rs of accretion indicated by rows of 



fiattcned bead-like nodules. 



