LAND PLANARIANS. 103 
nals, natural size. The same process of strobilation has 
been carefully observed by Graff in Microstomum lineare 
Oersted. In the chain of four individuals (Fig. 67) I indi- 
cates the division of the first order, and II those of the 
second order ; at the points in the zooids marked III there 
are indications of a future third subdivision, and at IV of 
a fourth ; so that potentially the chain con- 
sists of sixteen zooids, and the division is 
first indicated in the digestive tract which 
forms subdivisions with septa reaching to 
the body-walls, while secondary and tertiary 
mouth-germs appear in the division-sections 
{m', m", Fig. 67), 
Huxley in his Manual of the Anatomy of 
Invertebrated Animals states that in some 
genera of Turbellarian worms “‘a difference 
is observed between the eggs produced in 
summer, which have a soft vitellime mem- 
brane, and those produced later. These so- 
called winter ova have hard shells. 
The genuine flat-worms are divided into 
two suborders: Rhabdocela and Dendrocela. 
In the former group there is an extensible 
pharynx, and the digestive tract is not 
branched. The Rhabdocela are represented 
by Catenula, Prostomum, Microstomum, etc. 
The Dendrocewla sometimes have two tenta- 
cle-like continuations of the front end of the 
body. The digestive canal has one anterior, two 
posterior large, and many secondary branches, _ yg. 67.—strobi- 
and a proboscis. Here belong the Planarians S400," jglfaivi- 
of fresh and salt water, and the Geoplanida 7m lineare.—At- 
or land-planarians, represented in the United 
States by Rhyncodesmus sylvaticus Leidy. The only para- 
sitic species of the order known are Stimpson’s Cryptoce- 
lum opacum, which infests the sand-cake (Zchinarachnius 
parma), and Typhlocolax acuminata, which lives on a Holo- 
thurian (Chirodota) ; while Semper has described Anoplo- 
dium Schneideri, which lives in the intestines of Stichopus 
