34 
the brain area (these represent then the cerebral clusters), beneath 
the tentacle rudiments (as very distinet groups) and along the 
margin of the body. The diffusely scattered eyes between the 
cerebral eye-clusters and the marginal ocelli are then to be regarded 
as „frontar* eyes. 
The location of the genital pores in the family Stylochidae. 
Since Meixner 1907 published his valuable treatise on Styl- 
ochines, our knowledge of the interesting and very natural family 
Stylochidae has considerably inereased. The genera that have last 
been brought into this family are treated by Bock, 1923 b. 
1 have made a list, which cannot, however, be 
published because of lack of space, of all that is known 
to date about the location of the, genital pores in this 
family. Quoting a great many figures in such a table 
might perhaps give an idea of more exaetness than 
is actually valid for animals with a body as easily 
contracted as that of Polyclads. The relative figures 
computed from the table and given below are then 
rext-fig. 11. 
Pigment cups 
of ttntacular 
eyes, to show 
how diffe- 
rently orien- 
lated the 
eyes are. The 
dotted eyes 
do not 
belong to 
the tentacu- 
lar group. 
The arrow is 
drawn on the 
median side 
of the eye- 
group. 112 X. 
more significant, although even these may to a cer- 
tain extent be influenced by differences in contraction 
of different parts of the body. But owing to the great 
consistency of the body just oceurring in the Stylochids 
and the faet that the power of contraction is remark- 
ably less in Stylochids than in many other Polyclads, 
the figures have a greater validity than could be ex- 
pected from a mere knowledge of f. i. the Leptoplanids. 
Collectively they are of great aid in showing an un- 
mistakeable tendency in Stylochids to move the genital 
pores toward the caudal end of the body. 
I must here emphasize the absolute necessity of 
using direct measurement. In a modern treatise it is not sufficient 
to say, as has actually been the case, that the genital pores are 
„near the posterior end“ or „between the pharyngeal chamber and 
the posterior body end“, for such statements are rather useless 
in the diagnosis of species. 
Group I. In the genus Stylochus with its 24 identifiable 
species the distance between the female aperture and the posterior 
