750 PROFESSOR J. STEPHENSON ON 



Physiologically, also, the contractile activities of the two systems are closely 

 connected. In the middle and posterior parts of the animal, the contractions of the 

 two systems are fundamentally the same thing, a somewhat feeble contractile wave 

 affecting only the vacuole-like spaces of the circulatory system, while a stronger 

 contraction of the same nature manifests itself as an antiperistaltic wave of the 

 intestine. And where, in the oesophageal region, the two systems are becoming 

 anatomically and physiologically differentiated from each other, there is still a want 

 of definiteness about the result, as evidenced by the difference at various times in the 

 direction of the " heart's " contractions, and in the relation of these to those of the 

 muscular wall of the stomach. 



Vejdovsky (54, p. 21) describes certain " shining spindle-like bodies, appearing 

 to consist of single cells," which are shown by him in his pi. i. fig. 5, as oval or 

 spindle-shaped cells, suspended in the middle of the lumen of the "heart" by fine 

 strands attached at each end to its dorsal and ventral walls respectively. They are 

 doubtless the same as the strands or septa traversing the lumen of the "heart" which 

 I have mentioned above. 



It is presumably to these strands that Beddard (3, p. 180) refers when he says: 

 " In several species there is a row of somewhat fusiform cells in the dorsal vessel, which 

 have yellowish fat-drops in their interior. I have suggested that these cells probably 

 represent a rudimentary dorsal organ such as is found in the Enchytrseidse." 



Now the dorsal organ, or cardiac body, of the Enchytrseidse is a cellular rod 

 attached to the ventral side of the dorsal vessel and appearing in a transverse section 

 as a mass of cells projecting into the lumen of the vessel from its ventral side, and 

 not attached at all to the dorsal wall of the vessel ; this structure, Beddard considers, 

 may have originated from a dorsal diverticulum of the gut, comparable to the paired 

 dorsal diverticulum of Bucliholzia, which has become solid. It does not, however, 

 seem easy to compare a number of isolated strands, traversing the whole lumen of the 

 vessel, and attached to its dorsal as well as its ventral wall, Avith a solid cell mass 

 projecting upwards from the ventral wall and having no attachment to the dorsal 

 wall of the vessel. 



An alternative view has been indicated above. Regarding, with Vejdovsky 

 (54, p. 115), the vascular network of the intestine as the principal component of 

 the vascular system of the Oligochaeta ; and recalling the fact that in the iEolosomatidse 

 and Enchytrseidse the vascular network or sinus is present alone in the intestinal 

 region, while in other families a dorsal vessel is present in addition, it seems 

 permissible to regard this vessel, in the families where it occurs, as a differentiation, 

 a specialised track, of the network. On this view the strands passing across 

 the lumen of the " heart " of A^olosoma would be conceived as vestiges of the partitions 

 existing in an original lacunar system ; and the presence of the strands would be an 

 argument for the primitive character of JEolosoma — not, as on Beddard's view of their 

 nature, an argument in the contrary sense. 



