52 LEPADID.E. 



rudimentary state of the only organ of sense supplied by 

 it, namely, the eye, which in size and general appear- 

 ance has retrograded to the state in which it was in, 

 during the first stage of development of the larva; — I 

 have used the term embryonic, because, in the embryos of 

 ordinary Crustacea, all the ganglia are at first longitudi- 

 nally distinct, and laterally quite separate. The conclusion 

 at which we before arrived from studying the metamor- 

 phoses, namely, that the whole peduncle and capitulum 

 consisted of the first three segments of the head, is beauti- 

 fully supported by the structure of the nervous system, 

 in which these parts are seen to be supplied with nerves 

 exclusively from the supra-cesophageal ganglion : now in 

 ordinary Crustacea the supra-cesophageal ganglion sends 

 nerves to the eyes and the two pair of antennas correspond- 

 ing, as is known by embryological dissections, to the first 

 three segments of the body. Moreover, it is asserted that 

 the carapace which covers the thorax in Crustacea, is not 

 formed by the development of the first segment ; and this, 

 likewise, may be inferred to be the case with the pe- 

 duncle and capitulum in the Lepadidae, as the nerves 

 of the ophthalmic ganglia go exclusively to the eyes. 

 Finally, I may remark that in Pollicipes, looking to the 

 whole nervous system, the state of concentration nearly 

 equals that in certain macrourous decapod crustaceans, 

 for instance the Astacus marinus, of which a figure is given 

 by Milne Edwards. 



Olfactory Organs. — In the outer maxillae, at their bases 

 where united together, but above the basal fold separat- 

 ing the mouth from the body, there are, in all the genera, 

 a pair of orifices (PI. X, fig. 16); these are sometimes 

 seated on a slight prominence, as in Lithotrya, or on the 

 summit of flattened tubes (PL X, fig. 17), projecting up- 

 wards and towards each other, as in Ibla, Scalpellum, 

 and Pollicipes. In Ibla these tubular projections rise from 

 almost between the outer and inner maxillae. It is impos- 

 sible to behold these organs, and doubt that they are of 

 high functional importance to the animal. The orifice leads 



