REPORT ON THE NEMERTEA. 115 



about one-half of the thickness of the body-wall of the animal, and though somewhat 

 differently magnified, the position of the nerve-stem and of the layer cm may easily 

 guide us how to combine them. 



It is then seen that in PL VI. fig. 9 the longitudinal trunk, situated in the circum- 

 oesophageal blood-space, is not only cut through, but that even more than one nephridial 

 lumen (nep) appears in this section, showing that there is a doubling or at least a 

 branching of the principal nephridial duct in this region. Internal openings of this 

 system, funnels or anything comparable to them, were not detected by me in Eupolia 

 giardii or any other Eupolia ; there were, however, very definite bends at right angles, 

 piercing first the inner longitudinal and then the circular muscular layer, next the 

 nervous plexus, and then arriving in the outer layer of longitudinal muscles. In this 

 position the deferent branches of the nephridial system are seen in fig. 5, PI. VII., 

 which, moreover, reveals the important fact that sometimes more than one of them is 

 found at exactly the same level. I could not make out whether this duplication is in 

 any way related to that of the longitudinal tube ; I can hardly conceive it to be so, the 

 increase of the number of deferent vessels being also noticed in other cases, though hardly 

 as a regular phenomenon. In Eupolia giardii, too, I find it to be exceptional in this 

 sense, that most of the deferent ducts are single ; one section of another species ( Cere- 

 bratidus truncatus) contains the double duct on both sides, making the exceptional 

 phenomenon at the same time symmetrical. The number of deferent ducts observed in 

 the Challenger specimen of Eupolia giardii is seven on the right and five on the left 

 side, the latter being opposite to and symmetrically placed with five out of the seven on 

 the right. These numbers, however, only apply to that portion of the trunk behind the 

 head which was transversely cut, and belongs to the same series. I have not followed 

 up the nephridial apparatus to its posterior portion, but we may feel assured, on the 

 authority of Oudemans' researches, that it will on the whole answer to the diagram 

 given on pi. i. fig. 11 of his treatise. One point deserving mention is that the first 

 trace of the nephridial apparatus of this Eupolia is visible in about the ninetieth section 

 behind the tip of the snout. When I add that the upper brain-lobes occupy sections 

 25 to 45, the forward extension of the nephridia can more easily be imagined. Nothing 

 special can be said of the deferent or of the principal ducts but that their epithelium is 

 distinctly one cell thick, nucleated, and unmistakably ciliated. Nor have I any special 

 discoveries to record with respect to the nephridial system of any of the Challenger 

 Schizonernertea, and may refer the reader for certain specific peculiarities, number and 

 disposition of deferent ducts, &c, to the description of the species where I have embodied 

 these details when they did not appear to have any general significance. 



I should like, however, to refer a little more fully to the conspicuous development 

 at which the main, longitudinal canal of the nephridia has arrived in a certain species 

 of Cerebratulus (Cerebratidus macroren), where its walls are unusually massive (PI. 



