TRANSACTIONS OF THE SECTIONS. 117 
generation. I am well aware that the high authority of Prof. Milne-Edwards has 
asserted, that they are of no other use than to excite the female, in his ‘ Histoires 
des Crustacés,’ ‘‘ Ces appendices paraissent devoir servir ἃ diriger les verges vers les 
vulves, et peut-étre aussi ἃ exciter ces derniers organes,”’ which he has since repeated 
in the ‘Cyclopzdia of Anatomy and Physiology,’ article Crustacea. But I have 
myself repeatedly taken Carcinus Menas in the act of copulation, in which these 
styliform processes were deeply inserted into the vulva of the female. Since which 
time it has been my object to make out the anatomy of the organ as distinctly as 
possible, for which purpose I have dissected Cancer Pagurus, Xantho rivulosa, Por- 
tunus puber, Carcinus Menas; in the whole of which, and I doubt not but also in 
the remainder of the Brachyura, the internal organs lie folded upon themselves, one 
on either side of the stomach, each of which continues to the first joint of the fifth 
pair of legs, through the membranous portion of which in some—while in others a 
separate orifice exists through the calcareous portion of the leg—a membranous tube, 
the vas deferens, passes out, and is continued externally until it is inserted into the 
second joint of the first pair of the so-called false feet, through which it passes and 
ultimately opens at the extremity. For many days may the male be seen running 
about holding the female by one or more of his legs, pressing the carapace against 
its sternum ; this continues for a period more or less long, until the female throws 
off the exuvize, when copulation immediately ensues, face to face, and continues from 
eighteen to twenty hours, or perhaps until the new shell becomes sufficiently calcified 
to act as a protecting skeleton. 
V. Number of Broods from one Female in one Season.—! have been induced to be- 
lieve that crabs, like some insects, have more than one brood from a single impreg- 
nation of the male; the facts which incline me to this idea are, that in the month of 
May last I took a female, to the false feet of which were still attached the hair- 
like threads, the ‘external case of the ova, showing that the larva had been but 
recently let free, whereas upon dissecting the crab I found the uterus gravid with 
ova in an early stage of development. Upon considering, as before-mentioned, that 
impregnation takes place immediately after the period of moulting, and that the exuviz 
are cast but once in the year, I can only imagine that in the brood after the first, the 
ova are fertilized by spermatozoa retained within the cul de sac of the parent from the 
first or previous inoculation. 
VI. On the uses of the Fifth Pair-of Legs in the Anomoura.—The fifth pair of 
legs in the Anomoura are apparently useless, appearing as if formed by an arrest 
of development, which altogether incapacitates them from assisting in the office of 
perambulation. These, which in the Brachywra are connected with the last annular 
segment of the thorax, in the 4nomoura belong to the first segment of the abdomen, 
and generally lie folded up and at rest on either side of the carapace. 
In both the Brachyura and Macroura, within the branchial chamber are organs 
whose office is chiefly to excite currents over the surface of the gills, as also 
(probably) to remove any irritating substance which may have been brought 
in by the aérating fluid; these organs are called the flabelle, which, though 
common, I believe, to all of the above-named sections, yet in the dnomoura are 
wanting. This absence of an important agent in respiration, entails upon the animal 
death by asphyxia much more rapid, which still would be increased but that the 
office is partially fulfilled by the fifth pair of legs, which are, when required, inserted 
beneath the carapace into the branchial chamber ; and this is assisted by a peculiar 
power which the crabs of this order possess, in being able to raise up their own 
carapace ; a power of which they take advantage when respiration is impeded, in 
order to admit a greater body of water into the gill-chamber, but which is precluded 
from entering into the thoracic cavity by a thin membranous wall which unites the 
carapace with the sternum and abdomen at the inner wall of the branchial chamber. 
Neither is this the only purpose for which the fifth pair of legs serve in the economy 
of these crabs ; they are invariably supplied with strong cilia at the extremity, which 
also is sometimes didactyle, the prehensile form being obtained by the last joint being 
arrested in its development, impinging upon a process or excess of development of 
the penultimate; with this didactyle and brush-like extremity I have seen the 
Pagurus Bernhardus mop every joint in succession, and when required, cleansing the 
brush in the pedipalps. This pair of legs also carries the male organs of generation. 
