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IV. On the Hairs of Carcinus mænas. By W. CARMICHAEL M'Ixrosn, M.D., F.L.S. 
Communicated by T. S. COBBOLD, M.D., F.L.S. 
(Plates XIX. & XX.) 
Read December 4th, 1862. 
THE peculiar appearances presented in certain hairs of Carcinus menas, remarked in 
the course of other observations on the same animal, prompted the following inquiry, 
which, although it may not have revealed anything very striking, nevertheless appears 
to possess some interest, inasmuch as it demonstrates the varied aspects assumed by the 
hairs in a single species, which, again, may be regarded as typical of the brachyurous 
Decapods. However simple and superficial the investigation may seem, it is by no 
means an easy matter to give an account of the manifold diversities in the form of the 
hairs even on a single organ, and when the inquiry is extended to the whole body, it is 
impossible to compress it into a very small compass. 
Fresh and living specimens, as well as spirit-preparations, were used in the examina- 
tion; for the remarkable tenacity of life enjoyed by this Crustacean rendered its safe 
transportation a matter of ease and certainty, existing as it does for about a month ina 
botanic vasculum, either with or without alittle damp sea-weed. Peculiarities in different 
individuals, as regards presence or absence, thickness and length of the hairs, of course 
abounded; yet, throughout all the specimens of this species, a wonderful sameness in the 
essential structure of the hairs in like situations prevailed. 
I shall commence with the examination of the 
Hairs of the Eyes (Pl. XIX. fig. 4).—The calcareous cone which supports each compound 
eye has a regular circlet of hairs on the outer or convex side, which lends to it a peculiar 
interest. They are short, branched, closely packed together, and slant in general towards 
the apex of the eye. I have elsewhere* stated that these hairs “ present a most remark- 
able microscopic appearance, and one which strikes the investigator of the vertebrate 
forms with astonishment. The peculiarity of structure is not so much in the hair itself 
(confining this description solely to the hairs on the circlet of the eyeball), as in certain 
curious appendages which adapt it to its varied functions.” The hair is of the usual 
chitinous nature, and pale, “ with a light-coloured central space apparently filled with a 
semigelatinous substance. Its surface is almost everywhere clothed with growths of a 
fungoid appearance, some presenting the form of a floating mass attached to the surface of 
the hair by a filiform pedicle, whilst others are of a delicate, filmy structure, not tapering, 
of a pale-greenish hue, and having the aspect of pigmy fungi. Many are thickened and 
roughened with a black cohesive substance which entirely obscures the normal structure 
of the hair, allowing it to glance through only at intervals; while the dark parent mass 
appears in striking contrast with the filmy appendages, which glisten as they stretch from 
* Observations and Experiments on the Carcinus menas, p. 15. 
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