MACDONALD ON HETEEOCTATUUS AND SIPUNCULUS. 



81 



the body was lined with a ciliated membraue, which was reflected round 

 the larger branches of a transparent (probably water) vascular sys- 

 tem running along the spirally coiled intestine, with its singularly 

 constructed central suspensory ligament. All this militates against 

 the supposed JUchinoderm nature of Sipunculus, and give it radiating 

 affinities with the Annelida, Polyzoa and Tunicata, though perhaps 

 only of a representative kind. The simple anatomy of the larval 

 form, the Atlas of Peron, if it be not indeed a permanent one, is also 

 of great importance in this connexion. 





'//jih 'Ml . 

 5^ 



Eefekences 

 I. Sipunculus Heterocyafhi, (natural size) 



a. Opercular disk. b. caudal disk. 

 a. Opercular disk. b. caudal disk. c. proboscis, 



2. Ventral view enlarged. 



3. Dorsal view enlarged, a. Opercular disk. b. anus. c. proboscis. 



4. Corallum, seen from above, enlarged, a. Columella, b. primary, c. secondary 

 and rf. tertiary rays. e. primary. /. secondary and g. tertiary loculi. h.h.h. Open- 

 ings communicating with the burrow. 



5. Lateral vicAv, shewing a. the aperture of the biuTow. 



[The case of parasitism here descrilied has an especial interest if viewed in 

 relation to the apparently anomalous characters of the palfeozoic Pleuro diet yon, which. 

 we are much inclined to regard as a coral perforated in a similar manner. — Eds.] 

 N, H. R.— 1862. G 



