302 Dr. Strahl on the Limits of the Brachyura. 
mura, somewhere in the vicinity of the Dromide; in any ease 
it forms a particular section, on account of the position of the 
female sexual organs. 
The external antenna is not suspended immediately from the 
cephalothorax, like the internal antenna, but by means of an 
articular piece, which is called article basilaire” by Milne- 
Edwards in the Macrura. This articular piece is not a complete 
ring, but only a half-ring, which moves by its ends in a hinge- 
joint, and fulfils a°\double function. It not only bears the ex- 
ternal. antenna with its subsidiary organ, the antennal scale, 
but also contains the efferent orifice for the secretion of Suckow’s 
gland. The latter point has been confirmed by the malforma- 
tion discovered by me, and described in Reichert and Du Bois- 
Reymond’s ‘Archiv’ (1859, p. 833), but I wait for further 
corroboration. In all Macrura and Anomura this articular piece 
possesses a tubercle, which is perforated at the summit and closed 
by a membrane, the so-called tympanum. But this tympanum 
has a slit in its centre, which may be opened and closed by 
muscular action. This slit leads, by a tube of greater or less 
length, to the so-called auditory vesicle, which collects the secre- 
tion of the green gland. 
. This structure is shown by the articular piece throughout, 
even if the antennal scale be entirely wanting, as in the Palinu- 
ride, the Scyllaride, the Galatheide, the Porcellanide, the Hip- 
pide, and the Raninidz, In the Porcellanide this piece is still 
of considerable size, but in the Dromide it becomes so shrunken 
that essentially only the tubercle remains, but this fully de- 
veloped. In Dromia the tympanal membrane is very small, 
but still the slit is apparent; and Grapsus sensu strictiore has 
the same structure. The Brachyura show no trace of antennal 
scale ; and from the Dromide to them is only a step, Thus, if 
we imagine the slit in the tubercle of Dromia carried out to one 
side, so that here the peripheral margin is completely separated, 
we have the operculum of the Brachyura in its perfect form : 
for this operculum by no means possesses a construction com- 
parable to that of the stapes in the auditory organs of the higher 
animals ; it is rather a valve, which is attached externally to the 
pterygostomium, and can be opened in the direction of the me- 
dian line of the animal; its opening and closing is subject to the 
will; and for this purpose the operculum possesses on its inner 
margin a manubrium ascending into the interior of the animal, 
to which the muscles are attached. I have fully investigated 
this structure in both Carcinus Menas and Platycarcinus Pagurus; 
and found in these also that a reservoir is reached, likewise si- 
tuated in front of the stomach, and connected with a glandular 
organ, which is the apple-green organ (Suckow’s gland). 
