29 



on the analogy of Balanoglossus, must be regarded as a blood-space (fig. 1 8 1 , per. jr.) It will 

 be seen from longitudinal sections (PI. l\^ Hg. 33) that the pericardium more or less overlaps 

 the tip of the notochord, which, in sections in other planes, may accordingly he completely 

 encircled by the pericardium (PI. XII, fig. 160). 



The proboscis-pores, which are invariably two in number, have a constant relation to 

 the pericardium (PI. X, fig. 112; PI. XI, figs. 137, 138;/./.). The pore is in reality a tube 

 of appreciable length ; and in consequence of this fact Spengel (93, p. 470) prefers to term 

 it the "Eichelpforte" (in Balanoglossus). In Cephalodiscus (figs. 112, 138) the epithelium of 

 the tube which is situated nearer the middie line closely invests the wall of the pericardium. 

 The outer part of the epithelium is intimately related to the anterior dorsal horn of the collar- 

 cavity (1^. c.' a.~). 



In sagittal sections (PI. XII, figs. 147, 14S, /./.;-.; fig. 150, /././.) it is seen that 

 the direction of the tube is not vertical to the surface, but that it has an oblique course, the 

 internal opening being dorsal to the external opening. The latter is situated close to the base 

 of the first arm (PI. XII, fig. 158), and slightly on its median side. The proboscis-pores 

 traverse a part of the central nervous system, which is thus divided into an anterior and a 

 posterior portion in any sagittal section passing through a proboscis-pore (figs. 42, 151). 



Masterman (03, p. 717) has described the proboscis-pores as opening into the outer ends 

 of a transverse, crescentic furrow of the epidermis which he terms the "ectodermal pit". It is 

 easy to find specimens of Cephalodiscus shewing appearances which resemble Masterman's 

 figures. Thus an "ectodermal pit" is obvious in PI. XII, fig. 149; but I find that in this 

 particular case, the proboscis-pore does not open into the continuation of the pit or furrow, 

 but distinctly in front of it. In other cases (PI. V, fig. 45), the relations are reversed, and a 

 similar furrow is seen in front of the region where the proboscis-pore opens to the exterior. 

 Remembering the extremely muscular character of the proboscis and collar I am inclined to 

 think that these furrows are not constant structures, but are merely the result of crumpling of 

 the skin caused by contraction. 



Glomerulus. 



I have previously stated (97, p. 345) that there appears to be some indication of a 

 structure corresponding with the proboscis-gland or glomerulus of Balanoglossus ; and Masterman 

 has recently (03, p. 720) described the organ in detail. I have nothing to add to Masterman's 

 account, and I have indeed not obtained any preparations which shew its relations so clearly 

 as are indicated in his figures. Although I think it is probable, as M.asterman states, that it 

 contains blood-spaces by means of which the pericardial sinus (PI. XI, fig. 12,'è, per. s.) com- 

 municates with other parts of the vascular system, I cannot obtain any certain evidence on 

 this point. 



The glomerulus [gl.) is shewn in PI. IV', fig. 42 (C. dodecalophus), PI. VUI, fig. 93 

 (C. sióogae, neuter) and PI. X, figs. 113, 114 (C. IcvinseniJ ; and its wall is doubtless to be 

 regarded as a derivative of the epithelium of the anterior body-cavity. 



