300 ON HETEROPSAMMIA MICTIELINII, 



a long way from the burrow.. They are of such extreme fineness 

 that only a very thin bristle will penetrate them. 



The coral animal does not seem to suffer from the intruder, but 

 the base is swollen and distorted, sometimes projecting very 

 much at the aperture of the burrow, and often at right angles to 

 the major axis of the calice. In the only specimen in my 

 possession in which the curve of the burrow is not sinistral, the 

 whole base and sides are riddled with the smaller perforations 

 leading from the main passage. I counted no less than 24. As 

 the members of all this family of corals have their walls perforated 

 the filaments probably do no more than to enlarge the openings 

 they find. They have all a radiated circle of laminae round the 

 outer orifice, like- the groovings of the main aperture but much 

 more marked. I have never seen a specimen of Lobopsammia, no 

 matter how young or how small without these parasites, and from 

 the subsequent growth it would certainly seem as if the secretion 

 of strong matter were made in view of the requirements of the 

 parasite. Knowing how polyps can bear with indifference all 

 kinds of cutting and wounding, everything in fact except removal 

 from the water, it does not surprise us to find that these corals 

 can tolerate such exorbitant lodgers without injury to themselves. 



Keferences to Plate XV. 



Fig. 1. — Sipunculm heterocyathi, nat. size; a. — opercular disk; b. 

 caudal disk. 



,, 2. — Ventral side enlarged ; a. and b. as before ; c. proboscis. 



„ 3. — Dorsal view ; a. and b. as before ; c. anus. 



,, 4. — Corallum seen from above, enlarged ; a. aperture of 

 burrow ; b. c. d. first, second, and third orders 

 respectively ; e. f . g. corresponding loculi ; h. h. h. 

 openings connected with the burrow. 



,, 5. — Side view of corallum; a. aperture. After J.D. Macdonald 



