ANNELIDES. 
289 
excretion, which, in many Trematoda, discharges itself at the posterior 
end of the body, and which also pushes out its contents backwards, — 
an action often mistaken for the laying of eggs. Each stump of a 
foot consists of three parts, the last of which is furnished with four 
retractile horn-like hooks. By these feet, this parasite reminds us of 
the lower Crustacea, but it cannot perhaps be united to them, because 
the vibratile organs, which cover the superior surface of Myzostomum are 
altogether foreign to the Crustacea, insects, and Arachnida . — Leuckart 
describes another species, under the name of Myz. costatum : Corpore 
depresso, ovali margine crenulata, dorso costato ; acetabulis suctoriis 
hamuliferis separatis, acetabulis utrinque 4 et hamulis in utroque latere 
5 ; hab. in mari rubro, Comatulse multiradiatse parasitus. — A third spe- 
cies, Myz. glabrum, has the following diagnosis : — Corpore orbicular!, 
dorso convexo et marginibus glabris, infra concave ; acetabulis in utro- 
que latere 5, hamulum simplicem emittentibus ; hab. in mari Mediter- 
raneo, Comatulas mediterraneae (europaeaB) parasitus. This species varies 
from Myz. cirriferum almost only by the absence of cirri ; and Leuckart 
himself has some doubt of these two species being distinct, since it is 
improbable, that two quite ditferent species of a parasitic genus, should 
live upon one and the same animal in different seas. He also hazards a 
conjecture, whether the presence of cirri may not perhaps point only to 
a youthful condition. The reporter is convinced, that Myz. glahrum 
and cirriferum belong to one species, and that the former is an indi- 
vidual in which the cirri have shrunk, or become otherways lost. He 
infers this, from a specimen which he has taken from a Comatula euro- 
pcea at Cattaro, in which, besides the five pairs of stumps of feet, he 
distinctly recognised four pairs of acetabula, which Loven likewise saw, 
and Leuckart had probably overlooked ; and the margin of the disc of 
which he found covered with twenty very small projections, which the 
reporter supposes may be the shrunk or cast off cirri. 
A work of Duvernoy, which, according to its title (Considerations sur 
les Animaux Articules, sur les limites de ce type, et sur la place qu’il 
#doit occuper dans les cadres de la methode naturelle. Paris, 1841), 
should contain only general remarks on the Annelides, has not yet come 
to hand. 
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