160 TRANSACTIONS OF THE [FEB. 8, 



along the entire length so that respiration maj'- be carried on 

 by the part of the bod\^ inserted in the shell. Lying between 

 the umbilicus of the Gastropod shell and the undegenerated 

 right side of the hermit-crab, there is a constant stream of water 

 from the gills of the latter. 



In the commensal annelid described by Andrews,* the Poly- 

 dora perforates the umbilicus in several places. In the instance 

 above cited there is but a single opening between the smaller 

 coils and umbilicus. This was observed in a number of cases, 

 but there was no sharply defined boring. Wirenf has described 

 with great precision the variety Nereis fucala inquilina com- 

 mensal with Eupaijurus Bernhardus L. from the zoological sta- 

 tion at Kristineberg. Nereis fucata is recorded from Scandi- 

 navia, Great Britain and the French coast, and it has been 

 observed with hermit-crabs in mollusk shells b}^ Quatrefages| and 

 Johnson. § This species was supposed, till carefully studied, to 

 be the free living form which had sought refuge in the empty 

 shell. Wiren demonstrated characters of varietal rank. 



The Nereid living with the Pacific coast hermit-crab is an 

 undescribed species, but approaches very nearly to Nereis 

 fucala, while Eupagurus Bernhardus is given as the t^^pe to 

 which E. alaskensis (Benedict) belongs. || 



These facts signify that from several possible hermit-crabs and 

 from several possible Nereids, we find those two Puget Sound 

 species in commensalisra which are nearest to the Eupagurus 

 and Nereis messmates of Scandinavia. 



A somewhat similar case is that of Terehella and Harmolhoe 

 mentioned above (p. 153). Commensalism between _these two 

 genera has been noted on the Coast of France (Saint Joseph).^ 

 The Puget Sound Terebellid builds a different opening to his tube 

 from T. conchilega of the European coast, and has not the crim- 

 son ventral pLates. The tubes are of similar material in both 

 cases. Living in these tubes is the apparently peaceful mess- 

 mate, Harmothoe, the Pacific species somewhat diflferent from 

 the European. 



If this commensalism be monophyletic, the occurrence on op- 

 posite sides of the world, of nearly identical forms living to- 



*Amer. Naturalist, Vol. xxv., p. 25. 



tOm en hos erem. lefv. Annelid. Bihang K.Sv. Vet. Acad. Hand. Bd. 14, aft. iv. 

 No. 5. 



X Hist. nat. des Annelid. Ti. p. 548. Paris, 186.^. 



I Cat. Brit, non-parasitic worms in the Coll. of the British Museum, p. 159. London, 

 186.5. Ann. Mag., Nat. Hist., Vol. lii. p. 295. 1839. 



II A detailed comparison of these two species of annelids is given in contribution 

 No. 4. of this series. 



H Annales d. Science Naturelles t. 5, 1887, p. 149. In Terebella tubes have also been 

 found Aetinca nobi/is by Lankester in .Journ. Linn. Soc. VIIL, 1S(;5, and Poiyno- 

 Scolopendrina (Mcintosh) Report of Brit. Ass. for Adv. ot Science, 186H, p. 70. 



