84 THE VOYAGE OF H.M.S. CHALLENGER. 



" On the right side, the appendages of this large Crustacean present nothing abnormal; 

 the protocephalic member or appendage of the first ring of the head usually forms an 

 ocular peduncle ; the deutocephalic member consists of an antennule, and the appendage 

 of the third somite is the large or external antenna. On the left side, the second and 

 third appendages are symmetrical ; but the ophthalmic somite carries instead of an eye, 

 a long multiarticulate filament, resembling the terminal flagellum of an antenna. The 

 ophthalmopod has been preserved in its ordinary character at the base : even at its 

 extremity a rudimentary cornea exists, from the centre of which the flagellum to which 

 I allude originates and extends to the length of about four centimetres. It is multi- 

 articulate and furnished with hairs upon the superior and terminal portion, like the 

 inferior flagellum of the antennule. 



" I know of no other example of a transformation of this kind among the Crustacea 

 or other Articulata. A number of monstrosities occur in the formation of dactyli 

 or phenomena of the same kind ; but I have never seen an appendage present its 

 normal form on one side of the body and revert on the opposite side to the characters of 

 another organ. The interesting point to which I desire to draw the attention of 

 zoologists is not only the novelty of the occurrence, but also because it shows that in the 

 animal kingdom a kind of phenomena similar to those that we see in vegetables often 

 exists. 



" When a leaf is transformed, it may be into a bract, a sepal, or a petal, &c, or 

 when a petal or a stamen may mutually revert to a leaf-like condition, these transfor- 

 mations realise in the animal as well as in the vegetable kingdom, the theoretic view 

 relative to the fundamental origin of parts susceptible to a reversion of different char- 

 acters, and on this subject I may recall the fact that among certain Crustacea, the 

 dactylos of the first pair of pereiopoda becomes normally multiarticulate and antenni- 

 form. The genus Mastigopus of M. Stimpson offers us a remarkable example." 



Palinurus, Fabricius. 



The genus, as restricted by Dr. Gray and Dana, is here confined to those species which 

 Milne-Edwards ranges under the head of " Langoustes ordinaires," in which the most 

 apparent characteristics are the presence of a small central rostriform tooth or tubercle 

 that overhangs but does not cover or enclose the ophthalmic somite, which is generally 

 calcareous, the form of the somite of the first pair of antennae which is anteriorly pro- 

 duced and laterally compressed in front (as shown in the accompanying woodcuts taken 

 from the type of the genus), and the shortness of the flagella belonging to the first pair 

 of antennae. 



Geographical Distribution. — The genus as restricted in this description appears to be 

 confined to the northern hemisphere, Palinurus vulgaris, which is the type, is found on 



