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nuchal tentacles or at least nuchal tentacular groups as a feature 
met with in the Acotyleans. The weight of the character is thereby 
indicated. Stylochoides is an exception to the rule, but in this 
Cotylean the finger-like and ocelli-provided tentacles, though removed 
from the margin, lie nearer to the margin than to the brain and 
consequently cannot be regarded as true nuchal tentacles. As can be 
expected from the other organization, margo-tentacular eyes are 
present. The Acotylean Cestoplana has a peculiar arrangement of 
the eyes (cf. Bock 1913, pp. 56—57) which deserves further in- 
vestigation. 
Seeing how general the occurrence of tentacular groups of 
eyes is in the Acotylea, one is consequently a little suspicious of 
exceptions recorded, and before accepting them, one will ask for a 
thorough examination of the case. It is of course possible that 
tentacular eyes and tentacles may disappear, and this is perhaps 
the case in Bergendalia. The lacking of eyes in Plehnia arctica 
seems to be such a feature of total loss of eyes, or at any rate 
loss of their pigment cups, demonstrating that reduction actually 
takes place. 
Remarks on the male apparatus of the Stylochids. 
The Stylochidæ present considerable interest, as they show a 
great variability with respect to several characters and at the same 
time rich possibilities of combination. Since the different organs 
in diverse stages of specialization or reduction are combined with 
each other, the result must be that the types of organization are 
highly multiplied and makes it necessary to distinguish a greater 
number of genera. Taking the organs separately, one finds it an 
easy task to arrange a sequent series of the types of each organ- 
development. We have, for instance, a nice series of intermediate 
links in respect to the prostatic vesicle (= vesicula granulorum), 
from the highly specialized State in Stylochus to nearly total dis- 
appearance of this organ in Enterogonia. The development of 
tentacles, pharynx, and alimentary system, seminal vesicles, penis, 
vagina, Lang’s glandular vesicle, and uteri; the arrangement of 
eyes, the location of testes and ovaries, the position of genital 
pores, and so on, present a considerable variance. 
But the series do not run parallel in the genera. The blending 
