CHARACTERISTIC DEEP-SEA TYPES. — WORMS. 58 
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 cheetopods of the collection. The existence 
of cheetopods in certain localities where the animals themselves 
are not found may be inferred by the presence of their tubes. 
Like the littoral species of Maldanidee, Clymene, Serpule, 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 ¿hat 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. 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. 203. — Hyalopomatus 
Eschrichtii. — 1. glutinatrix. Langerhansi 4. 
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 erustacean. 
live ; they are mainly built up of pellets 
