ORGANIC DEPENDENCE AND DISEASE 
57 
are silicious sponges allied to the living Enplectella or 
Venus’s Flower-basket, and though we find no parallel ex- 
pression of commensalism in the living glass-sponges, yet 
Euplectella carries a parasite in the form of a crustacean 
which in youth enters its 
open cloacal cavity and re- 
mains there so that when the 
sponge has in adult growth 
built the terminal or sieve- 
plate over its aperture the 
crustacean is wholly and 
permanently caged. 
This ancient association 
continued long after the 
Paleozoic, for I have else- 
where illustrated its occur- 
rence in the sponges of the 
Cretaceous from very strik- 
ing specimens sent to me by 
Dr. F. A. Bather of the Brit- 
ish Museum. They are here 
reprinted. All show a spiral 
worm tube encircling the 
long median cloaca of the 
sponge, in one the spiral be- 
ing dextral and the other 
sinistral. The flat section 
here shown is a direct photo- 
graphic print made from a 
thin slide and shows the 
actual distance of the annelid tube from the cloaca, and 
suggests also the presence of other commensal worms in 
the upper left-hand part of the sponge-body (prepared by 
Doctor Bather). All are from the Chalk series at Beck- 
hampton. 
Fig. 43. A silicified sponge from the 
English Chalk exposing a spiral 
worm tube encircling the wall of 
the cloaca of the sponge. ( Courtesy 
of Dr. F. A. Bather. ) 
