woodworth: planktonemektes agassizii. 3 



The soundings given above indicate the depth at wliich the dredgings 

 were made with an open trawL 'J'he colors given in quotation marks are 

 from notes taken by Alexander Agassiz on board the Albatross, and refer 

 to the living animal. A water color drawing made by Mr. Agassiz of the 

 living animal represented in Figure 4 shows the color as light brilliant 

 scarlet, the intestinal diverticula and proboscis showing as bands of 

 deeper color. The shape of the living animal as indicated by the sketch 

 was like that of many of the larger marine Turbellaria, with parallel 

 undular sides, and bluntly rounded at both ends. 



All of the specimens except No. 2 (Fig. 2), which was not sectioned, 

 proved to be females. In specimen No. 4 (Fig. 3) the ovaries were 

 slightly developed, and could be seen only in sections. In the other 

 three specimens the ovaries were prominent even before the specimens 

 were subjected to a clearing reagent. Both specimens of Pelagonemertes 

 taken by the Challenger were also females. 



The chief differences between Pelagonemertes and Plank tonemertes 

 may be summarized as follows. In Pelagonenjertes there are distinct 

 openings for the mouth and proboscis, the former being ventral, the 

 latter terminal ; the dorsal cerebral ganglia are much laiger than the 

 ventral pair; the vascular system does not include a median dorsal 

 vessel ; the intestinal tract is comparatively simple, i. e. with few lat- 

 eral diverticula, five and thirteen in the two specimens so far known. 

 In Planktonemertes there is a common external opening for mouth and 

 proboscis, slightly subterminal in position ; the dorsal pair of brain gan- 

 glia are much smaller than the ventral pair; the vascular system in- 

 cludes a dorsal median vessel, which extends in the posterior portion 

 of the ventral wall of the rhynchocoelom, and unites with the lateral 

 vessels at the posterior end (this is seen in Figure 3) ; the intestine bears 

 a great many (more than 50) lateral diverticula, and so profuse is the 

 dendritic branching of these that in a transverse section the body ap- 

 pears to be honeycombed with cavities of varying size and outline, the 

 gelatinous mesenchyma being but slightly developed. 



A detailed study of this interesting form has already been made, but 

 will be delayed in publication until the completion of the report upon 

 the other Nemerteans taken by the expedition. 



Museum of Comparative Zoology, Cambridge, Mass., 



May lOtli, 1899. 



