102 ZOOLOGY. 
The Turbellaria are hermaphroditic, the ovaries and testes 
with the accessory apparatus (Fig. 65) being present in the 
same individual; but in many forms the sexes are distinct. 
Little is known of the development of the flat-worms. 
In a common marine Planarian, Stylochus elliptica (Girard), 
which is about two centimetres long, and lives under stones 
between tide-marks, north of Cape Cod, the eggs are depos- 
ited in May and June, in a thin, viscid band, on stones and 
sea-weeds. The eggs undergo total segmentation in four or 
five days after they are laid. The larva is round, ciliated, 
with a caudal flagellum. In eight or ten days after the 
larva has hatched, it stops swimming about, and becomes a 
“mummy-like body,’? which Girard calls a ‘‘ chrysalis.’’ 
In this state it floats about in the water. Its further his- 
tory is unknown. 
In Leptoplana (Polycelis), according to Keferstein, the 
yolk undergoes total segmentation as in Stylochus, the 
outer layer of cells forms a blastoderm which surrounds the 
more slowly growing cells within. Keferstein describes 
and figures the various stages by which the spherical cili- 
ated embryo attains the form of the adult, whose devel- 
opment seems to be less in the nature of a metamorphosis 
than that of Stylochus. 
The Planarians also in some species mul- 
tiply by fission, and when cut into pieces, 
according to H. J. Clark, each piece may 
eventually become a well-formed Planarian. 
Clark figures in his ‘‘ Mind in Nature’? two 
Planarians derived from two sections of 
Dendrocelum lactewm, which became fully 
developed within eleven days after the opera- 
tion. Several Turbellarians are known to 
undergo spontaneous fission. 
Catenula lemne Duges, by transverse di- 
Fig. 66.—Catenu- vision, forms chain-like aggregations, and 
fa quaterna unaer- a South African species, C. quaterna, of 
—After Schmarda. Schmarda, has been found by him to have the 
same habit. Fig. 66 represents two individuals (much 
enlarged) in partial division, and a chain of five individ- 
