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



known to M'Intosh, Graff, and other observers, and which I have again met with in 

 the Challenger Hoplonomertea, cannot be more circumstantially described. Moreover, 

 the stylets in the different Hoplonemertea did not offer any remarkable deviation from 

 the well-known type, and though the transverse sections gave very clear detads regarding 

 the arrangement of the muscle-fibres in the muscular bulb, about the epithelium of the 

 glandular duct that conveys the probably venomous secretion of the posterior cavity to 

 the base of the stylet, &c, these are only confirmations of facts already known and 

 need not be recapitulated here. The shape of the stylets was mentioned when the 

 species were described; those of Drepanophorus, though not obtained from an actual 

 Challenger specimen, are represented in the woodcut on p. 16. 



The muscular walls of the proboscis differ in the various genera, and these differences 

 speak for themselves when we compare figs. 11 and 12 of PI. II., and figs. 1, 2, and 5 

 of PI. III. (Carinina), fig. 11 of PI. VI. (Eupolia), fig. 7 of PI. VIII. (Pelagonemertes), 

 fig. 6 of PI. XII. (Amphiporus) , and figs. 2 and 3 of PI. XV. (Cerebratulus). These latter 

 show the muscular layers of the proboscis of the Schizonemertea to be a repetition of the 

 muscular layers of their body-wall : a circular layer between two longitudinal ones, the 

 circular layer giving off fibres at diametrically opposite poles to the external membranous 

 sheath (b), and moreover, a nervous plexus (n.pl), which is also situated between the outer 

 longitudinal muscular coat y' (that just below the epithelium), and the circular one ft'. 

 This nerve-plexus does not go all round, at least it cannot be distinctly made out except 

 throughout one-half of the circumference. It is also traversed by radial fibres, and is again 

 replaced by definite longitudinal stems when we examine a transverse section of the 

 proboscis further back (PI. XV. fig. 3). These longitudinal stems are characteristic of 

 certain species of Cerebratulus, and a plexus, even a far more complete and cylindrical 

 one than the one figured (PI. XV. fig. 2) for Cerebratulus macroren, is characteristic of 

 others. The nerve-stems enter the proboscis at its point of insertion, and spring from 

 the right and left extremity of the ventral brain commissure. 



In the posterior regions of the proboscis of Eupolia, of Pelagonemertes, and of nearly 

 all the other species, the musculature appears to be reduced to a simple longitudinal 

 layer, carrying the epithelium on one side, and being held together by an ensheathing 

 membrane on the other (PL VI. fig. 11, and PL VIII. fig. 7). 



In Carinina there is an additional circular layer, and the remarkable fact, which has 

 been already noticed above, of the situation of the nerves still enclosed in the epithelium. 



In Amphiporus, Drepanophorus, and Pelagonemertes (anterior portion) the 

 proboscis-wall exhibits the notable complications corresponding with the curious dis- 

 position of the nerves in the proboscis, and which was described in sufficient detail 

 by M'Intosh (beaded layer) (XIX, XX), myself (IX), von Kennel (XVI), and 

 Graff (HI). To von Kennel the merit is due of having definitely established 

 the nervous significance of the parts in question. The innervation may here be 



