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



accessory to the sense-organs forming the system of the lateral line, a sensory epithelium 

 being protected by and combined with them, has no direct parallel in Arwphvporus 

 moseleyi, although it cannot be denied that the flask-shaped glands are in the immediate 

 vicinity of and on a level with the lateral nerve-trunks. 



The absence of these glandular structures in the Palseonemertea and Schizonemertea 

 hitherto observed, renders the suggestion of any close homology very hazardous. Still, 

 I would not wholly refrain from pointing out the distant kind of parallelism which may 

 be noticed, and which has certainly contributed to induce me to consider these 

 organs in the paragraph devoted to the sense-organs, a proceeding which future inves- 

 tigations may perhaps show to have been wholly unfounded. The significance of this 

 parallelism will once more be discussed, when, in the chapter of General Considerations, 

 there is further scope for speculation. 



PROBOSCIS AND PROBOSCIDIAN SHEATH. 



Concerning this important organ, so very fully described by MTntosh in his 

 Monograph on the group (XIX), the Challenger material has not revealed any startling 

 peculiarities. Nevertheless, it deserves some closer consideration, because certain points, 

 e.g., the exact mode of the anterior attachment of the proboscis in these worms, could 

 be studied more favourably by me in certain of the Challenger sections than ever 

 before. Moreover, the Russian naturalist Salensky has lately 1 propounded certain 

 views concerning the proboscis and its sheath which deserve consideration and refutation. 



I will first describe the facts with respect to the proboscis which we notice in the 

 Challenger Nemertea. 



Carinina has a proboscis which, in transverse section, reveals the remarkable 

 peculiarity that the primitive order of succession, according to which in the body-wall 

 we meet with (1) integument, (2) longitudinal nerves, (3) musculature, also obtains in 

 the proboscis, the innervation of which takes place through the intervention of two 

 longitudinal nerves, which are so situated as to be enclosed by the internal cellular 

 epithelium (PI. II. figs. 11, 12), just as is the body nerve-stem in a section of the 

 trunk. This fact, though it cannot be looked upon as a direct confirmation of the 

 hypothesis advocated by me after I had become acquainted with Graffs Monograph 

 on the Rhabdoccela, viz., that in the Nemertea also the proboscis should be looked upon as 

 a gradual derivative of an original continuation of the body-wall, which has become 

 introvertible like the snout of the Rhabdoccela proboscidea, still throws a very favourable 

 light on these views. And this is further the case when we notice that in many Schizo- 

 nemertea there is also an order of succession of the layers in the proboscis-wall which is 



1 Zeitschr. f. wiss. ZooL, Bd. xliii. p. 509. 



