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VII.— On - the so-called “ Auditory-sac ” oe Cirripedes. By 
Charles Darwin, F.B.S. 
In my work on Cirripedes I have described an orifice, previously 
unobserved, beneath the first pair of cirri, on each side of the body, 
including a very singular elastic sack, which I considered to be an 
acoustic organ. Furthermore I traced the oviduct from the peduncle 
to a mass of glands at the back of the mouth, and these glands I 
called ovarian. Dr. Krohn has recently stated that these glands 
are salivary, and that the oviduct runs down to the orifice, which I 
had thought to be the auditory meatus. It is not easy to imagine a 
greater mistake with respect to function than that made by me; but 
I expressly stated that I could never succeed in tracing the oviducts 
into actual union with these glands; nor the supposed nerve from 
the so-called acoustic sack to any ganglion. As Dr. Krohn is no 
doubt a much better dissector than I am, I fully admitted my error 
and still suppose that he is right. Nevertheless, several facts can 
hardly be reconciled with his view of the function of the several 
parts. To give one instance: if any one will look at the figure of the 
Anelasma (Lepadidse, PI. iv.), he will see how extremely difficult it 
is to understand by what means the ova coming out of the orifices 
( e ) above referred to, could be arranged in the symmetrical lamellae 
which extend up to the summit of the capitulum: it must be 
observed that the ova are united together by a delicate membrane en¬ 
closing each ovum ; moreover the cirri in this animal are in atrophied 
condition, without regular articulations, so that it is inconceivable how 
the ova can be transported and arranged by their agency. 
I have lately received from an eminent naturalist, Prof. F. de 
Filippi, a paper (Estratto dall’ Arch, per la Zoolog. 31st Dec. 1861), 
chiefly devoted to the development of the ova of Cirripedes, in which 
the following passage occurs :— 
“ The small size of Dichelaspis Darwinii has not enabled me to 
verify the relationship discovered by Krohn between this problem¬ 
atical organ and the termination of the oviduct; but on the other 
hand the transparency of the tissues has enabled me to perceive a 
peculiarity of structure which may help to elucidate the question. 
Fig. 13 represents what I persist in calling a hearing organ. Within 
a cavity, tlie walls of which are united to the surrounding tissues, 
there is a pear-formed sack or ampulla. On the neck of this am¬ 
pulla, at a, are numerous minute lines parallel to each other and to 
the axis of the ampulla. I doubted at first whether the appearance 
of these lines arose from folds in the membrane, and therefore I 
separated some of the sacks, and I could then better convince myself 
that these lines correspond with true nervous fibres, thin and simple, 
embedded in the rather thick, resisting, and transparent substance 
which forms the walls of the ampulla. This circumstance seems to 
me to show clearly the sensitive nature of the organ, and hence to 
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