some new Species o/ Drawida. 503 



bej'ond somite 20. A supra-intestiual occasionally and 

 a subneural vessel never present. Both the dorsal and 

 ventral vessels are full of muscular fibres and the pheno- 

 nienou of the walls of the heart becoming opaque on pouring 

 spirit on freshly opened specimens, observed in D. grandis, 

 liourne, is shared by the dorsal vessel over the gizzards in 

 this species and in D. elegans. The degree of development 

 of vasa vasorum in the walls of the heart diminishes as we 

 go forward and it is also present in the walls of the ventral 

 vessel, which picks up opacity under the spirit, though to a 

 less extent. I have been unable to discover any valves in the 

 course of the principal vessels, and the internal endothelial 

 layer in the dorsal and ventral trunks may be thrown into 

 folds simulating a valve-like structure in the regions anteiior 

 to somites 10, where the mesenteries are thickest. It is also 

 in this part of the body that the powerful muscular con- 

 tractions, while burrowing or otherwise, are likely to reverse 

 the course of the blood-flow, and hence the need for valve- 

 like structures. The lumen of the arterial twigs going to 

 the enteric appendages is partially divided longitudinally by 

 a ridge-like elevation of the internal lining. This partial 

 division perhaps represents an incipient stage in the morpho- 

 logical differentiation of the vessel into afferent and efferent 

 ducts. The only other region where I have noticed a valve- 

 like fold is the point where the enteric twigs are given off 

 either directly from the longitudinal dorsal vessels or from 

 the appendicular branches. The valves are simple folds of 

 endothelium pointing towards the blood-flow. The lateral 

 longitudinal vessel supplies branches to the anterior nephridia 

 and all the reproductive organs and their associated glands. 

 From the ventral vessel are derived branches for the nervous 

 system, the bod^^-wall, and the ventral walls of the intestine 

 and the nephridia. 



Nephridia. — I have only to add here that the vesicle 

 described as occiirriiig in D. grandis, Bourne, is not present 

 in this and other species, except D. paradoxa, described in 

 this paper, and the narrow ciliated tubules form com[)licated 

 loops in the periphery of the lobes, which, however, can be 

 easily made out from the plexuses of blood-capillaries. The 

 vesicles in these species bear the same microscopic structure 

 as the lobes, hence they are described as being absent as 

 such. The glandular part is disposed in distinctive lobes, 

 the enteric lobe lying on the sides of the intestine, the sub- 

 enteric below the intestine, and the parietal projecting into 

 the sides of the body-cavity. In the species of Drawida 



