394 
POPULAR SCIENCE REVIEW. 
« gorged with an inextricable mass ” of branching ovarian tubes, 
filled with immature ova and a granular matter. These are 
gathered together into two main ducts, which run on either side 
in the peduncle to join two glandular masses of an orange colour, 
and of the thinness of a wafer, described by Darwin as “ gut- 
formed bodies,” whicli embrace the stomach. These, which 
were believed by Cuvier to be salivary glands — organs which 
have no existence in the Cirripedia — are ovaries. Since 
these important glands have, oddly enough, no oviducts, how 
do the ova get into the ‘‘ sack ’ of the animal ? Just before 
the Cirripede changes its coat (“ Exuviation ”), which it does 
frequently, being a “ very growing ” animal, the ova burst 
from the tubes in the peduncle, and, after being carried along the 
main “ lacuna,” which serves for the circulation of the blood, are 
collected — how ? it is not known — in the cellular “ corium ” 
underlying the body-“ sack.” Eventually the ova, aggregated 
by a modification of the corium into two “ lamellae,” become 
adherent to certain “ ovigerous froena,” which are a pair of 
folds of skin depending inside the sack on each side of the 
attachment of the body. Now these folds, though thus 
specialised, serve, together with the whole surface of the body 
in these gill-less Cirripedes, for respiration ; but in the sessile 
forms their homologues, in the shape of a much-folded mem- 
brane communicating with the circulating channels and having 
no “ ovigerous ” function, were held to be gills by Professor 
Owen. Here is a remarkable instance of the “ Transition of 
organs,” for Darwin has no doubt “ that the two little folds of 
skin, which originally served as ovigerous froena — but which 
likewise very slightly aided the act of respiration — have been 
gradually converted by natural selection into branchiae, simply 
through an increase in their size and the obliteration of their 
adhesive glands. If all pedunculated Cirripedes had become 
extinct — and they have already suffered far more extinction 
than have sessile Cirripedes — who would ever have imagined 
that the branchiae in this latter family had originally existed 
as organs for preventing the ova from being washed out of the 
sack ? ” 
No heart has been discovered in any of the Cirripedes. The 
blood circulates in lacunoe^ or channels not defined by distinct 
walls, the principal one of which has a kind of valve to pre- 
vent regurgitation of the blood into the body during the 
contraction of the peduncle. 
The nervous system ordinarily consists of a chain of six 
ganglia, or nerve centres, from which nerves radiate. Two 
of these become fused together in Pollicipes, and in some of 
the sessile Cirripedes the concentration proceeds as far as in 
