BY REV. J. E. TENISON-WOODS, F.L.S. 299 



begin to assume a more orderly arrangement, and finally form 

 into closely set rings of minute and recurved hooks reaching to 

 base of the oval tentacula." 



Dr. Macdonald adds, this parasite is evidently closely allied to 

 the little animal from the Indian Seas, named Zithodermis cuneus, 

 by Cuvier, and which was the only species known to him. He 

 further adds that in the coral borers, which are identical with the 

 little animals here noticed, he found that the oesophagus was 

 encircled by a narrow collar, with a cephalic enlargement on 

 either side, from which tentacular nerves arose, and in contact 

 with which dark eye specks were distinctly visible, there is also 

 a single ventral nervous chord giving off lateral nerves at stated 

 intervals, but without any very apparent ganglionic dilatations. 

 I observed moreover that the cavity of the body was lined with a 

 ciliated membrane, which was reflected round the larger branches 

 of a transparent f probably water) vascular system, running along 

 the spirally coiled intestine, with its singularly constructed central 

 suspensary ligament. All this militates against the supposed 

 Ecliinoderm nature of Sipunculus, and give it radiating affinities 

 with 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. The editors of the Review 

 also express their opinion that the paleozoic Pleurodictyon is a 

 coral perforated in a similar way. 



By referring to my figures of Psammoseris cylicioides in last year's 

 Proceedings, (PL 1.) it will be seen that one of the specimens is 

 clearly burrowed by the same Sipunculus, (fig. 2). All the other 

 specimens were noted on univalve shells much longer than the 

 corallum. Perhaps it is in this way that the animal seeks 

 protection from the boring intruder. I imagine that the asperities 

 on the body of the Sipunculus must give rise to filaments of 

 considerable length, because the perforations extend sometimes 



