23 
ioplana, Copidoplana, and Tripylocelis belong to the Family Lepto- 
planidae, which has highly varying genital organizations, but in 
a limited degree. 
All the genera mentioned lack Lang’s glandular 
ve side! In this respect the Family Leptoplanidae is oF particular 
interest. This very natural Family, with the limitation that I gave 
it in 1913, contains Polyclads with a very characteristic habitus. 
A great number oF species inhabit the temperate and warm seas, 
and they show as a rule a wealth oF specimens. IF, as is Frequently 
the case, the external Features do not give suFficient characteristics 
For the different species, a condition that already caused Lang to 
desist From making any determination without a sectional exami- 
nation (Lang, 1884), an examination oF the copulatory apparatus, 
which presents numerous types oF organizations, will provide good 
results. The male organ shows the greatest specialization, but the 
Female apparatus also presents no little deviation in different species. 
The greatest differences are Found just in respect to Lang’s glan¬ 
dular vesicle. It oFten occurs as a globular projection. At times 
it reaches extraordinary dimensions, Forming a long and wide sac 
(For instance, Notoplana atomata and australis, Zygantropland), but 
Frequently it shows degeneration, and may even in some species 
be entirely missing. A typical case oF reduction is seen in Noto¬ 
plana evansi Laidlaw in the shape oF a short duet with a barely 
noticeable caudal projection (Bock, 1913, text-fig. 35, p. 189). Its 
location here is particularly remarkable, as it lies immediately 
alongside the vagina. In the genus Stylochoplana, to which Cera- 
toplana shows such marked relationship, there is, as a rule, a 
Lang’s glandular vesicle, although oF small dimensions. Stylocho- 
plana pusilla From Japan (Bock, 1924, Plate, fig. 4) shows most 
clearly how close it really can approach to the Female gonopore. 
Under such circumstances it would seem quite plausible to consider 
the development oF a ductus vaginalis in conjunetion with the pre- 
existence oF a Lang’s glandular vesicle, and thus assume, that 
the ductus vaginalis has been derived From the duet leading to 
the Lang’s glandular vesicle. This duet Forms the direct continu- 
ation oF the inner end oF the vagina and runs in a caudal direction. 
Idioplanoides (Woodworthia) atlantieum (Bock, 1913, text-fig. 25) 
shows clearly how close this duet can lie to the vagina, with the 
