No. 426.] WEMERTEAN PARASITES OF CRABS. 449 
Gononemertes, although it still retains ocelli and has a central 
stylet in the proboscis. 
Summary. — The above observations seem to lead to the 
following general conclusions: (1) that the nemerteans inhabit- 
ing various species of crabs are distributed throughout the 
North Atlantic and into the Pacific Ocean, (2) that the New 
England form is identical with the long-known European 
species, (3) that several European forms thought to be widely 
different are either closely related or identical, (4) that a// the 
species recorded show great similarity of structure, and may be 
closely related, (5) that the worms are true parasites and are 
not found except on the body of their host, spending practi- 
cally their whole existence on the crab's body — in the gills 
when young, on the egg masses when mature, (6) that in dif- 
ferent geographical regions the same species of worm may 
infest different species of crabs, (7) that the worms crawl about 
on the bodies of the crabs and are thus easily transferred from 
one host to another, (8) that by means of the free-swimming 
embryos the species may be distributed widely, although the 
young usually remain among the egg masses until they are 
past the free-swimming stage. 
LIST OF REFERENCES. 
BENEDEN, P. J. VAN. 
1861. Faune littorale de Belgique, Turbellariés. Mém. Acad. Roy. 
Belgique. Tome xxxii, pp. 18-23, Pl. III, Figs. 1-30. 
BERGENDAL, D. 
1900. Ueberein Paar sehr eigenthümliche nordische Nemertinen. Zool. 
Anzeiger. Bd. xxiii, p. 321. 
BÜRGER, O. 
1895. Die Nemertinen. Flora und Fauna des Golfes von Neapel. 
`- Bd. xxii 
DIECK, G. 
1874. Beiträge zur Entwicklungsgeschichte der Nemertinen. Jenaische 
Zeitschr. f. Naturwiss. Bd. viii, pp. 500-520, Taf. XX, XXI 
Le laboratoire de Wimereux en 1888. 
