23 



Stjm.d.c.^ 



Alltenor 



Stomt 



The text-fitjure i is based on the sagittal section of an advanced bud of C. dodecalophus 

 shewn in PI. XIII, H_i^-. i8i. 

 The proboscis, the colhir and 

 at least half the alimentary 

 canal in this specimen have 

 a position which closely cor- 

 responds with the relations of 

 these parts in Balanoglossus. 

 The principal morphological 

 axis may be regarded as the 

 line of intersection of what is 

 marked as the "frontal" plane 

 with the sagittal plane of the 

 fiofure itself. It will then be seen 

 that in this figure the pharynx 

 [ph^i passes in an antero- 

 posterior direction, giving ofi' 

 the notochord {iich}^ forvvards 

 from its dorsal side, and passing 

 posteriorly into the oesophagus 

 [pes^ and stomach {sfoni.). This 

 organ has a conspicuous dorsal 

 caecum {stom. d. ^.), while a 

 smaller lobe extends a short 

 distance forwards ontheventral 

 side of the oesophagus. The 

 dorsal line of the metasome is 

 shortened, so that the intestine 

 {int.), which opens from the 

 second stomach {sto;n.~), passes 

 dorsall}- and a trifle forwards, 

 to open at the anus (a7i.) 

 which has been shifted into a 

 somewhat dorsal position. 



Comparing the text-figure with the sagittal section of the adult (PI. IV, lig. 42), in the 

 same species, it will be seen that the alimentary canal in its definitive arrangement has its 

 ventral flexure more strongly marked than in the bud. The morphologically dorsal surface of 

 the pharynx now faces, for the most part, posteriorly, and its ventral surface anteriorly, althougn 

 the part which immediately succeeds the mouth has its dorsal wall in its original morphological 

 position. The phan,'nx is in fact ~-shaped, a right-angled bend having been developed owing 

 to the ventral flexure of the alimentary canal. 



Fig. I 



Vential. 



— C. dodecalophus. Median sagittal section of an advanced bud (after PI. XIII, 

 fig. 181), to illustrate the terminology used in this Report. The anterior, 

 posterior, dorsal and ventral surfaces and the transverse and frontal 

 planes are indicated: — /., proboscis; ^., coUar; met.., metasome; I, 2 and 3, their 

 respective body-cavities; h.c.^b.., the part of the metasomatic cavity included in the 

 loop of the alimentary canal; /'., ventral lobe of proboscis; p.i.., its pigment-band; 

 /iv., pericardium; «/., mouth; .«ir/(., notochord; ///., pharynx; öfi., oesophagus; 

 stoin..^ stomach; stom. d. c, dorsal caecum of stomach; stoin.'^., second stomach; 

 int., intestine; /•., rectum; an.. anus; c.n.s., central nervous system; op., operculum 

 or lüwer lip; ov., ovary; st., stalk. 



