156 
In generalizing from a sparse number pf specimens or a single 
individual, one must, of course, be cautious in regard to this 
character as well as to others. Preferably the comparisons should 
be made between full-grown, sexually mature specimens. An agree- 
ment in every detail is scarcely to be expected, as a certain indi¬ 
vidual variation is present also here. 
With these reservations, I consider the arrangement of the eyes 
very usable for systematic purposes. I may here especially refer to 
the numerous species of the genus Prosthiostomum as good examples 
hereof. They demonstrate in an excellent way the value of this 
character for classification. And there the use of it has been ge¬ 
nerally accepted because the genital apparatus, male as female, 
presents a great conformity. 
Returning to the special conditions existing in Stylochidae, we 
find in this family so rich in species the following groupings of 
the eyes: 1) marginal eyes, 2) tentacular eyes, 3) cerebral eyes, 
and 4) frontal eyes. The discrimination of the last group is not as 
authoritative as in the case of the other three. 
Marginal eyes. These vary greatly within the family, both 
as to number and distribution. They occur along the entire margin 
of the body and in a particularly large number in Kaburakia, 
Enterogonia, Cryptophallus, and Parastylochus. In the genus Stylochus 
with its numerous species, several of these possess marginal eyes 
also along the entire margin of the body. They are more numerous 
and in several rows along the anterior margin of the body, but 
gradually diminish in number towards the posterior end of the body. 
This is, for instance, the case in Stylochus orientalis Bock, 
arenosus Willey, zebra Verrill, plessisi Lang, tauricus Jacubowa, 
hyalinus Bock, and marmoreus Bock. They are also found along 
the entire body-margin in Idioplanoides and Limnostylochus bor- 
neensis Stummer-Traunfels and annandalei Kaburaki. In the follow¬ 
ing species of Stylochus they do not reach the posterior end but 
cease at distances different according to the various species: cinereus 
Willey, ceylanicus Laidlaw, bermudensis Verrill, frontalis Verrill, 
nebulosus Verrill*), rutilus Yeri & Kaburaki, ijimai Yeri & Kaburaki, 
*) Verrill (1893) States that young specimens of Stylochus nebulosus 
possess eyes along the posterior margin, while in older ones they are lacking 
there. Such a statement calls for a renewed investigation, as generally the 
