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XVII. — On the Further Anatomy and the Budding Processes oj Cephalodiscus 

 dodecalophus (M'Intosh). By Arthur T. Masterman, B.A., D.Sc, F.R.S.E. ; 

 Lecturer and Research Fellow in the University of St Andrews. (With Five 

 Plates.) 



(Read 6th June 1898.) 



The former paper (5) on the Anatomy of Cephalodiscus was incomplete in certain 

 particulars, which I am now in a position to add. These are mainly in regard to 

 the alimentary canal, the nervous system, and the reproductive organs. To the 

 present description of these will be appended an account of the budding processes, 

 which are a very conspicuous feature of the species. 



It has been pointed out that the twelve plumes, which are definitely arranged and 

 spread out dorsally in front of the head region, have longitudinal grooves running down 

 their ventral side into the mouth region. " One cannot doubt that in Cephalodiscus 

 the cilia of the ventral surface cause currents down the ventral grooves of the plumes, 

 and thence into the mouth, .... carrying food-particles, entangled in slime, into the 

 alimentary canal, a mode of alimentation analogous to that of Phoronis, and indeed of 

 the Urochorda " (5). We might add to this, the Lamellibranchiata, Brachiopoda, and 

 Amphioxas. This characteristic method of ingestion by means of ciliary currents must 

 be regarded as a primitive one, and it is interesting to notice the several methods by 

 which the superfluous water current is got rid of, and the food retained. The primary 

 origin of gill-slits has been suggested by both Harmer and Brooks as connected with 

 this function. The single pair of pharyngeal clefts in Cephalodiscus certainly appear 

 to agree with such a theory. 



A series of horizontal longitudinal sections through an adult Cephalodiscus from 

 before backwards cut the front portion of the pharynx transversely and the hind part 

 longitudinally. Such a series may be seen in figs. 1 to 9. 



In fig. 1 it may be noticed that three oral grooves (l, 2, 3) converge from each side 

 of the mouth, passing downwards from the branchial plumes. They are directly 

 continuous with the grooves running down the ventral side of each of the plumes, 

 which unite in pairs to form the oral grooves here seen. 



The dorsal wall of the buccal cavity is quite simple, but on the ventral wall appears 



slight semi-circular depression. In fig. 2 this depression is observed to have divided 



into two grooves in the ventral surface of the pharynx, which deepen rapidly. In 



fig. 3 they present chordoid walls, and as far back as fig. 4, they can be readily 



VOL. XXXIX. PART III. (NO. 17). 4 G 



