EE POET ON TPIE CIEEIPEDIA. 
27 
III. THE CEMENT APPARATUS. 
The cement apparatus ancl the genital organs of the Cirripedia are in general 
tolerably well known ; in detail, however, our knowledge often proves to be very 
insufficient. Darwin has the merit of having discovered the presence of the cement- 
apparatus, but he failed to understand its organisation, partly because he confounded its 
elements with those of the female genital apparatus. 
Krohn 1 gives a much more accurate description of the cement apparatus of Lepas 
ancitifera and Conchoderma virgcitum. He was the first to observe the true cement- 
glands. In Lepas anatifera they are, according to him, situated in the most superior 
part of the peduncle, and scattered through the connective tissue which envelops the ovary ; 
they are very numerous, and they have the shape of long oval, vesicular little bodies, 
which are attached to very delicate and richly ramified canals in the same way as berries 
to their stems. These canals open, before the inferior extremity of the ovary is reached, 
into the two cement-ducts, the commencements of which are swollen into ampullse. 
These cement-ducts have been already observed by Darwin ; they run downwards at a 
considerable distance from one another, one at the right, the other at the left hand side 
of the peduncle, and they are situated close to the innermost layer of longitudinal muscle- 
fibres. Finally they penetrate into the cliitinous wall of the peduncle near the place 
where it is attached ; they pass through this wall, becoming narrower and narrower, and 
are then lost sight of. In the deeper layers of the chitinous wall of the peduncle the 
cement-ducts are invested with rounded swellings of different sizes, which are hollow 
and which are doubtless in open communication with the ducts ; these swellings act 
as reservoirs to retain the cement before it is evacuated. In Conchoderma virgatum the 
cement-apparatus differs from that of Lepas anatifera in the cement-glands being 
for the greater part placed in the parenchymatous tissue of the mantle and for a very small 
part only in the superior extremity of the peduncle. The two cement-ducts with their 
swollen ampullse reach very close up to the place where the capitulum communicates 
with the peduncle. The two ampullse in this genus communicate with one another 
by means of a transverse and tortuous canal. 
I studied the cement apparatus in Lepas , Conchoderma, and Scalpellum. As 
regards the histological structure of the apparatus my researches are far from satisfactory, 
the condition of the material at my disposal being, in part at least, the cause of this. 
The peduncle of the Cirripedia is very difficult to preserve ; even in specimens freshly 
sent over by the Direction of the Zoological Station at Naples, the condition of the 
tissue has suffered much. 
The little bodies which were considered by Krohn as the true cement-glands must 
1 A. Krohn, Beobachtungen iiber den Cementapparat und die weiblichen Zeugungsorgane einiger Cirripedien, Archiv 
f. Naturgesch. Jahrg. xxv. Bd. i. pp. 355-364, 1859. 
