462 PROCEEDINGS OF THE ACADEMY OF [June, 



only a trace of the dorsal presetal lobe, and the cirri are of larger size 

 than in the typical foot. The 2d bears still larger cirri, united with 

 the neuropodium, and the latter is still further reduced. The first 

 postbuccal somite bears a fully formed trilobate setigerous parapodiimi 

 like the second on the left side, and only a sim2:)le cirrus on the right 

 side. 



Toward the posterior end of the anterior region the base of the neuro- 

 podium increases, and the terminal lobes, especially the presetal, dimin- 

 ish in length. The neuropodial cirrus at the same time increases 

 until its tip reaches beyond any other part of the foot, while the ventral 

 portion of the neuropodium which bears it becomes partly cut off by 

 distinct anterior and posterior furrows. Meanwhile the notopodial 

 cirrus has become relatively shorter and stouter and its terminal part 

 slightly flattened antero-posteriorly. All of these changes become 

 progressively emphasized. Not till the 54th somite does the noto- 

 podium appear as a slender process arising in common with the noto- 

 podial cirrus, and reaching as far as the tip of the postsetal lobe, but 

 not to the end of the neuropodial cirrus. After its abrupt appearance 

 the notopodium becomes gradually shorter and more and more closely 

 united with the cirrus. Although from its beginning supported by an 

 aciculum the notopodium at first bears no setae, and even as far back as 

 the 65th foot only a single one has been detected. Indeed, throughout 

 the entire region notopodial setae are very few. 



No further important change occurs until somite LXXVI, when the 

 body rather rapidly decreases in diameter and assumes the Unear 

 character of the posterior region, while the parapodia increase in length 

 to 1^ times the width of the body, a change due in part to the larger 

 size of the neuropodium and notopodium, but still more to their eleva- 

 tion upon a common base. Taking the 100th parapodium as a typical 

 example the following description applies : Base of parapodium nearly 

 as deep as body, swollen with spermatozoa in the example studied, 

 as long or slightly longer than neuropodium, which is again longer as 

 well as deeper than notopodium, each of which divisions is supported by 

 a single rather stout, straight, tapering, yellow aciculum. Neuro- 

 podium divided into two rather short (the dorsalmost the longer), 

 pointed, presetal lobes, and a much broader, leaf-hke, postsetal lobe, 

 the somewhat shorter tip of which lies opposite the interval between 

 the shghtly divergent presetal lobes. Neuropodial cirrus elongated 

 conical, arising from a distinct base about the middle of the ventral 

 surface of the body of the neuropodium, its tip reaching to end of ven- 

 tral presetal lobe, from which, however, it naturally diverges ventrad. 



