VERMES AND MOLLUSCA OF THE DEEP SEA 113 



Each polypide is provided with a single pair of 

 large pinnate arms, resembling the arms of a 

 Brachioj)od, and a broad muscular epistome by means 

 of which it is able to creep up or down the tube. 



The affinities of this interesting creature are by 

 no means sufficiently well understood. It is one of 

 those forms that, without being, strictly speaking, 

 a connecting link between large and well-known 

 groups of animals, indicates to us some of the lines 

 of evolution that these groups may liave passed 

 through ; and, in so far as it does this, it has its 

 value and importance. 



Cephalodiscus, though related to Rhabdopleura in 

 the presence of a structure corresponding to the 

 arms, and a broad epistome, seems to be more closely 

 connected with such a form as Balanoglossus in the 

 presence of a single pair of gill-slits, a small 

 rudimentary notochord and the position of the central 

 nervous system.' 



Whatever position these genera may ultimately 

 occupy in our systems of classification, there can be 

 little doubt that much valuable information will be 

 obtained by a farther study of their structure and 



• A rudimentarynotocLord projecting forward from the buccal 

 cavity into the epistome has quite recently been discovered in 

 Rhabdopleura. 



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