ENTEROPNEUSTA HILL. 337 



As in other species, the "notochord" possesses a continuous wide 

 lumen, crossed here and there by cellular bridges, and reaching to 

 near its apex. Numerous glands open into the lumen along its 

 whole extent, but are specially abundant in the dorsal wall of the 

 neck of the " notochord." 



Proboscis Skeleton. The " end plate " (fig. 3, eps.) closely in- 

 vests ventro-laterally the posterior portion of the blind sac, which 

 here is somewhat quadrangular in outline (fig. 3, Ibs.) Behind, 

 the end plate narrows and passes over into the body of the pro- 

 boscis skeleton, overlying the posterior portion of the unpaired 

 ventral proboscis pocket. The body is at first convex below and 

 provided with short nearly vertical wings investing the " noto- 

 chord " laterally. Posteriorly the ventral surface of the body 

 soon looses its convex form, and behind the posterior end of the 

 ventral proboscis pocket is distinctly keeled. In sections just 

 behind the ventral proboscis pocket the entire skeleton is found 

 to consist of a dorsal flattened portion prolonged on each side into 

 short almost horizontal wings, below which is a blunt triangular 

 keel-like projection. In the dorsal portion, the lines of stratifica- 

 tion correspond with the ventral wall of the "notochord"; it thus 

 represents the "body " of the skeleton. In the ventral projection 

 the lines correspond in direction with the adjacent epidermis : it 

 thus represents the " keel" of the skeleton. 



In this species the " keel " is not separated from the " body " 

 by " chondroid tissue," and it is not provided with distinct lateral 

 outgrowths or wings. Posteriorly the keel gradually becomes 

 blunter and thicker and at the same time decreases in height, 

 until, at the level of the proboscis pores, the entire skeleton has 

 the shape shown in fig. 5. The skeleton (vps.) is here in section 

 again convex below, slightly concave above and provided with 

 two short ventrally curved wings. The skeleton continues in this 

 condition up to the point of union of the proboscis neck with the 

 inner face of the collar. Here the "nuclei" of the "legs" appear, 

 separating the now thin " body " from the ventral part of the 

 skeleton, the continuation of the "keel." Posteriorly the "nuclei" 

 eventually separate from each other to form the diverging "legs" 

 of the skeleton, which end considerably in front of the mid-region 

 of the collar. 



The " chondroid tissue " of the proboscis neck (figs. 2-4, ch.) is, 

 as in other species of the genus, not very strongly developed. 

 The cell strands penetrating it are derived mainly from the ventral 

 proboscis pocket, and also in lesser degree from the dorsal pockets. 



Heart-bladder. The heart-bladder has the usual relations. An- 

 teriorly (fig. 1, h.) it is prolonged down on each side of the "noto- 

 chord " so as to enclose about the upper three-fourths of the latter. 

 It does not extend quite to the extreme apex of the " notochord." 



