CHARACTERISTIC DEEP-SEA TYPES. WORMS. 53 



extend from the littoral region as far as the greatest depth here 

 recorded, one species having indeed been brought up in a 

 Dentalium shell from a depth of 1,568 fathoms. Although 

 so numerous, no new forms of these groups were collected 

 either by the " Challenger " or " Blake," with the exception, 

 perhaps, of some of the tubicolous types in deep water. Fur- 

 thermore, these groups have but a slight significance as com- 

 pared with the chsetopods of the collection. The existence 

 of chsetopods in certain localities where the animals themselves 

 are not found may be inferred by the presence of their tubes. 

 Like the littoral species of Maldanidse, Clymense, Serpulse, and 

 their allies, they must cover extensive tracts of ground with 

 their tubes. Yet such a conclusion is not always admissible 

 without further evidence ; it can be accepted only when the indi- 

 vidual worm builds his tube in so characteristic a way that there 

 is no possibility of mistaking it for that of other annelids. Sev- 

 eral times tubes which from their whole appearance have been 

 taken for worm-cases were discovered to be inhabited by crusta- 

 ceans (Amphipoda). We cannot always decide if the occupant 

 of the tube was also its builder. 1 When no foreign material is 

 used in the construction of the tube except mud consolidated 

 by the secretions of the worm, the tubes of very different spe- 



Fig. 261. Diopatra Fig. 262. Diopatra Fig. 263. Hyalopomatus 



Eschrichtii. . glutinatrix. Langerhansi. ^. 



cies of worms may have a great similarity among themselves ; 

 when, on the contrary, various foreign materials are cemented 



1 Prof. S. I. Smith has observed the of their excreta, cemented together by 

 peculiar tubes in which some amphipods threads spun by the little crustacean, 

 live ; they are mainly built up of pellets 



