92 THE VOYAGE OF H.M.S. CHALLENGER. 



(3) that in Cannina the opening through which the proboscis is everted lies ventrally to 

 this furrow ; (4) that in most CerebratuU the proboscidian opening would similarly lie 

 ventrally to the point of meeting of the lateral cephalic furrows if we supposed these to 

 meet at the tip of the snout ; (5) that in a few cases the opening appears to have shifted 

 into the central part of the fissure ; (6) that in other Cerehratuli the fissures, though 

 continued on the anterior and apparently truncated portion of the snout, do not wholly 

 fuse (PI. I. fig. 12), but that just in the interval the proboscidian opening is situated; 

 (7) that again in other CerebratuU this anterior truncated portion is wholly devoid of 

 any continuation of the fissures, which in their turn may be exceedingly deep and long 

 (PL I. fig. 16); (8) that in the Amjjhipori alluded to (PI. IX. fig. 9) the common 

 opening for proboscis and digestive cavity is also situated ventrally to the terminal fold ; 

 (9) that in Eupolia transverse and very shallow cephalic fissures are found, which very 

 strongly resemble those of the Hoplonemertea (even in the presence of short and numerous 

 secondary grooves perpendicular to the principal groove), and which similarly contain the 

 opening that leads into the posterior brain-lobe, as is the case in Carinina and the 

 Hoplonemertea, and that even yet in certain Eupoliae a trace of a terminal horizontal 

 furrow has been retained (PI. I. fig. 7). 



Tabulating these difi"erent facts, the case would appear to stand thus : — 



Carinella annulata, one terminal shallow horizontal groove, two transverse lateral 



ones, no cUiated canal. 

 „ inexpectata. (VIII) terminal groove uncertain, transverse lateral grooves, 



ciliated canals into the brain-substance opening out into these 



grooves. 

 Carinina, . . . terminal groove present, lateral grooves, with openings of 



ciliated canal leading into a separate posterior brain-lobe. 

 Amphiporus, . . terminal groove present, lateral grooves, with openings of 



ciliated canal leading into a separate posterior brain-lobe. 

 Eupolia, . . . hardly a trace of terminal horizontal groove, lateral grooves as 



in the Carinellidse and Hoplonemertea. 

 Valencinia, . . no grooves at all, simple round opening for ciliated canal. 

 Schizonemertea, . two longitudinal (never transverse !) cephalic grooves which in 



some cases are wholly separate, in other cases meet at the tip 



of the snout, and might then in their entirety be compared to 



a terminal horizontal groove such as that of Carinina. 



If the latter conjecture be true, i.e., if we may suppose the lateral furrows of the 

 Schizonemertea to be derived from an ancestral phase, in which a terminal groove like 

 that of Carinina was separated into two halves which deepened and widened on both 

 sides of the head, reaching down as far as the opening of the ciliated canal into the 



