490 Howard Edwin Eiiders. 



*'fans." The fans exhibit a continnal rhythmic movement that 

 usually sweeps the water towards the posterior end of the animal. 

 On account of their similarity in nearly every respect a description 

 of one of the segments will answer for the remaining ones. 



The fifteenth segment (fourth of the mid-region), when in the 

 middle of a beat, has the form of a broad bell. Its base, which is 

 directed toward the forward end of the body, is covered with the 

 delicate integument of the body. At some distance from and joarallel 

 Avith the periphery of the bell the integiiments of this base are 

 joined to the integuments of the top (i. e., posterior convex portion) 

 by means of delicate cross-strands of muscular tissue. This produces 

 on its anterior surface a shallow semi-circular furrow that is parallel 

 with the edge. The cavities which are found within the bell are 

 diverticula of the general cavity. Within the central portion is seen 

 the greenish tinted sigmoid curve of the intestine, and in the lateral 

 cavities are seen the vesicular portions of the third pair of nephridia. 

 The ventral side of the 'Hjell" rests with its whole length upon the 

 ventral longitudinal muscles in such a way that its rim surrounds 

 these muscles ventrally. Immediately posterior to this rim and in 

 the middle of the segment is a pair of thick spatulate appendages 

 which are directed posteriorly. The presence of several close-set rows 

 of brown uncinal plates on the distal margins of these neuropodia, 

 and an additional pair of small papillae, which bears uncinal plates, 

 near the ventral margin of the bell, confirms Laffuie's conclusions on 

 the homology of these segments with the other segments of the body 

 (page 267) : ''This papilla represents the external lobe of the ventral 

 ramus and is homologous with it. It is consequently the homologue 

 of the superior edge of the ventral suckers of the twelfth and thir- 

 teenth segments." ''The central part of the palette represents the 

 body of the animal, while the peripheral part is the homologue of the 

 ventral rami, rami which are fused to the walls of the body by their 

 inner face." 



The fourteenth segment (foremost palette) bears a small adhesive 

 disc of the same form as those of the twelfth and thirteenth seg- 

 ments. It is intermediate in structure between these and the large 

 neuropodia just described for the palettes. That it is homologous 



