Studies on Earthworms. - Journal of Cell Science

246 WILLIAM BLAXLAND BENHASI.
liani, Intraclitelliani, Postclitelliani, Aclitelliani, have already
been given above.
The extent of the clitellum varies considerably in the same
genus, even in the different specimens of the same species
when fully developed; for instance, in Lumbricus agricola
it occupies six or seven somites, xxx to xxxvi; in L. rubellus,
somites xxvi to XXXII (seven somites); in L. trapezoides,
somites xxvn to xxxv (nine somites); whilst in L. (Allurus)
tetraedrus it occupies only six somites, from xxn to XXVII.
Amongst the Intrachitellian forms the same variation is to
be noted : Anteus has as many as fifteen somites, xv to xxix,
making up the clitellum; Titanus has nine somites, xv to
xxmj Urochreta has ten somites, xiv to xxm; Geogenia
has ten somites j whilst Rhinodrilus has only three somites
iu this structure, xix, xx, xxi. It commences as far forwards
as somite ix in Geogenia.
In Eudrilus the three different species each have a different
number of somites in the clitellum, E. decipiens having only
three, XIII, xiv, xv; whilst E. Lacazii has six somites, XTII to
XVIII, to form this organ. In Rhinodrilus the girdle is complete,
whilst in the other forms it resembles Lumbricus in
having a saddle shape.
Amongst the Postclitellian genera there are usually fewer
somites occupied by the clitellum, which is a complete girdle,
and nearly always commences with somite xiv (Perichseta,
xiv, xv, xvi; Plutellus, xiv to XVII; Acanthodrilus, xiv
to XVII, and others), or in XIII (Perionyx, XIII to XVII, and
Pontodrilus, xni to XVII); in xn, in Kinberg's genera
Rhodopis and Mandane, or in xv, in Pontoscolex. (In
Kinberg's genera, Nitocris, Amyntas, Lampito, Pheret
i m a, the clitellum appears to commence at somite xiv, and
this character with the numerous setse to each somite would
justify us in considering them as forms of Perichasta.)
Rhodopis, if Kinberg's description can be considered of
any value, possesses the shortest clitellum, occupying only two
somites, as is also the case in Perichseta bicincta.
The position of the clitellum and the position of th'e gizzard