DR. W. C. M‘INTOSH ON THE HAIRS OF CARCINUS MJENAS. 81 
or pinched, little or no movement of the limbs results; but irritation of the hairs above 
mentioned on the larger appendage of the internal antennze immediately causes convulsive 
startings and intense commotion. When the Crab is swimming in the water, it is very 
apparent that these organs are of great moment to the animal, and they constantly move 
with a jerking vibratile action, by which the hairs may be used to the bestadvantage. On 
being interfered with, these antenne are immediately withdrawn, while the external, 
which want the same development of hairs, move but little. Instead of its having, like 
the Lobster, antennz possessing only a sparse distribution of hairs at the joints, there 
exists in this animal and in its allies an immense aggregation of peculiar hairs at a single 
part, which have a direct and special connexion with the soft parts in the interior. 
M. Lavalle was amongst the first to point out the fact that the hairs of Crustacea have 
a special connexion with the soft parts in the interior*. He was followed by Hollardt, 
and Hàckel in Müller's * Archiv.’ Neither of the latter, however, recognized any con- 
nexion between the shell and hair-canals and the soft vascular and nervous layer below 
the cuticle or chitinogenous membrane. The most recent observer on the subject is 
Mr. Campbell De Morgan 1, who more clearly defined the exact relation of the hairs in the 
Lobster, Shrimp, and Prawn with the inner integument, in which the nerves terminate. 
In regard to the organ under notice in C. m«enes, before becoming acquainted with the 
papers above mentioned, observing the great delicacy of the cuticular layer, and the 
position of the hairs of the terminal antennulze with regard to the pale granular matter 
contained therein, I had stated, “ May not these hairs resemble our finger-nails, in that, 
though quite insensible in themselves, they form a most accurate knowledge of the 
qualities of surrounding objects by the admirable adjustment of the nervous elements in 
proximity ?"$ Notwithstanding the greater number of joints in the external antenn:e, 
and their extensive powers of motion, they are somewhat rough tactile organs when 
compared with the internal, whose special hairs render them the most sensitive organs in 
the entire animal. Whether these hairs are solely connected with common sensibility, 
or are subservient to the exercise of a special sense in connexion with the basal organ, I 
have not been able to determine with certainty ||. gri 
Hairs of the Foot-jaws. 1. The External or Great Pair.—The hairs spring in a 
single row along the oral margin of a, fig. 1, but form a double fringe to the elongated 
* Ann. des Sci. Nat. 1847, 3° sér. (Zoologie), tom. vii. Speaking of the hairs of Decapod —- he says, “ils 
sont toujours en communication avec l'intérieur du test par un canal qui traverse en droite igs toute 1 Spun de la 
carapace, et qui est tantót vide et tantót rempli d'une matitre semblable à celle qui existe à l'intérieur des poils. 3 
t Revue et Magasin de Zoologie, 1851. + Phil. Trans. 1858, pp. 895-903, pl. 71. $ Op. cit. p. 4. 
|| This antenna is considered the auditory organ in this animal and its allies by Mr. Spence Bate (Ann. Nat. Hist. 
2nd ser. vol. xvi.), the principal argument of this excellent naturalist resting on the — (1) that the above- 
mentioned hairs are auditory cilia ; (2) that the calcareous “ chamber having walls" in the basal swelling is the cochlea ; 
(3) that in the external antenna “ there is no internal structure of any kind which could identify it as being an organ 
of sound.”  Unprejudiced by a knowledge of these arguments at the time of my first examination, I have found no 
reason as yet to alter my opinion as regards this animal, after repeated observations and experiments and when aware 
of the above views. In the first place, no proof has been found of the hairs being auditory cilia ne than 
olfactory cilia ; secondly, in the intimate anatomy of the basal swelling of the internal antenna, the delicate sac and 
the calcareous prominence do not favour the above supposition more than the other, in this animal 1 thirdly, in the 
cavity at the base of the external antenna there are otoliths or their homologues in Carcinus menas. : 
Dr. Farre is of opinion that the internal antenn are the auditory organs in the Lobster; and Prof. Huxley, who 
