80 



OLIGOCHAETA 



12. Vascular sinus of 



with alimentation converted into a quite different physiological path, and one which 

 must bear some relation to the vascular system. 



Now there is some evidence that the ' cardiac body ' of certain Enchytraeidae has 

 had a similar origin. In Biochholziu the paired dorsal diverticula of the oesophagus, which 



are comparable probably to the calciferous 

 glands of earthworms, are surrounded by 

 a blood-sinus where they are attached to 

 the gut ; this blood-sinus becomes further 

 forward the dorsal vessel ; there is thus 

 a diverticulum of the oesophagus, as it were 

 thrust into the dorsal vessel ; it is to be 

 pointed out in the first place that a dorsal 

 diverticulum of the gut never coincides 

 with a cardiac body ; Hoest was apparently 

 the first who compared the cardiac body 

 of the Chlorhaemidae with the gut diverti- 

 culum of the Enchytraeidae ; it is not in 

 my opinion a valid objection to this identi-! 

 fication to point out, as Cunningham has done^, the absence of any present connexion 

 between the cardiac body and the epithelium of the oesophagus ; such a communication 

 may easily have become lost ; there are plenty of analogous instances. If we imagine 

 the gut-diverticulum to lose its lumen a cardiac body is at once produced. We should 

 therefore look upon those forms which have a cardiac body a3 being more modified 

 than those in which there is a gut-diverticulum ; as in the genus Aeolosoma there is 

 a trace at least of a cardiac body, better marked in the perhaps allied' ttenocZriZus; 

 these genera are perhaps to be regarded as the descendants of genera in which there 

 was a dorsal diverticulum of the oesophagus — an argument for the non-primitive 

 character of Aeolosoma. It seems to me to be also possible that the blood- 

 glands of Fhreodrilus are referable to the same characteristic diverticula of the 

 oesophagus. The cells contained in the lateral vessels will be on this interpretation 

 the remains of the calciferous glands ; the vessel which contains them will be the 

 hypertrophied vessel originally supplying these hypothetical glands ; this may also 

 help us in understanding the anomalous presence of an intestinal heart in Branchiura 

 in the same segment as that which also contains a dorsal heart ; if the intestinal heart 

 be regarded as the last trace of a vanished pair of calciferous glands the difiiculty 



BUCHHOIZIA. CALCIFEHOUS GLAND. 

 (After Michaelseii.) 



I. Peritoneal layer. 2, 3. Tubules of gland 4. 

 Dorsal vessel. 5. Lumen of intestine. 6. Ventral 

 vessel. 7. Peritoneum. 8, 9. Muscular and epi- 

 thelial layers of intestine, 

 intestine. 



' On some points in the Anatomy of Polychaeta,' Q. J. Micr. Soi. vol. xxviii, p. 259, etc. 



