228 W. G. EIDEWOOD. 



and third plumes — the last concealed in the figure b_y tlie 

 second plume — are showing refractive heads {r.h.), and their 

 surface is no longer smootli, but warty ; tlie pinnules are 

 larger and more numerous than in l. The figure m, like i, 

 shows liow the ciliated groove between tlie two rows of pin- 

 nules of each of the plumes 1, 2, and 3 faces towards the 

 dorsal surface of the buccal shield. 



Figure n is a dissection made in the same manner as that 

 shown in figure J, by the removal of the buccal shield on the 

 one side of the collar and the '' body " of the bud on the 

 other. The preparation is viewed from the dorsal surface, so 

 that the grooves of the plumes are facing away from the 

 observer. The fifth plumes ai'e seen to be continuous with 

 the bases of the fourth plumes, and with the post-oral 

 lamella; they are unequally developed on the right and loft 

 sides of the body. 



In o the pinnules on the first plumes are now fiuger-like 

 processes^ those on the fourth are in the same stage of 

 development as the pinnules of the first plumes were in the 

 stage represented in figure m. There are twelve or thirteen 

 pairs of pinnules on the plumes of the first pair, and about 

 nine on the fourth plumes, but the numbers later become 

 increased by the development of new pinnules at the basal 

 end of each series. The fifth plumes arc larger than in the 

 last stage, and show an indication of pinnules, but as yet they 

 have no end-bulbs. There is no sign of a sixth plume 

 between the fifth plume and the post-oral lamella, o, like n, 

 is a dorsal view, and the ciliated grooves of the plume-axes 

 are not seen ; the grooves of the first and second plumes are 

 facing ventrally, those of the third ventro-latcrally, and 

 those of the fourth postero-laterally. 



Figure P shows an unequal development of the right and 

 left plumes of the fifth pair. On the right side the plume 

 has about eight pairs of pinnules and a moderatel}^ differen- 

 tiated end-bulb, whereas on the left side the length of the 

 plume is only a little greater than the width. The groove 

 on the right-hand plume is facing posteriorly. 



