OPHTHALMIC GANGLIA AND EYES. 51 



mitella I did not see the eyes ; but the ophthalmic gan- 

 glion consists, as I believe, of a single globular one, placed 

 exactly between the two globular, supra-cesophageal gan- 

 glia, all three being of nearly equal size. Professor Leidy 

 does not mention the ophthalmic ganglia; hence I infer 

 that in Balanus, which is a more highly organised Cirripede, 

 they are fused into the supra-cesophageal ganglion. 



In all the genera, the double eye is seated deep within 

 the body ; it is attached by fibrous tissue to the radiating 

 muscles of the lowest part of the oesophagus, and lies 

 actually on the upper part of the stomach ; consequently, 

 a ray of light, to reach the eye, has to pass through the 

 exterior membrane and underlying corium connecting the 

 two scuta, and to penetrate deeply into the body. In 

 living sessile Cirripedes, vision seems confined to the 

 perception of the shadow of an object passing between 

 them and the light ; they instantly perceived a hand 

 passed quickly at the distance of several feet between a 

 candle and the basin in which they were placed. 



As the infra-cesophageal ganglion sends nerves to the 

 tropin and to the first pair of cirri, it must correspond 

 to the segments, from the fourth to the ninth inclusive, 

 of the archetype crustacean. The state of the supra- 

 cesophageal and ophthalmic ganglia appears to me very 

 interesting : I do not believe that in any mature ordinary 

 crustacean, the first or ophthalmic ganglion can be shown 

 to be distinct from the two succeeding ganglia, or to be 

 itself composed of a pair laterally distinct. The ganglia, 

 corresponding with the second and third segments of the 

 body, which should normally support two pair of antennae, 

 are in the Lepadidse united together ; but laterally they 

 are generally distinct in outline, and are actually separate 

 in Alepas : the supra-cesophageal ganglion shows also its 

 double nature, by giving rise to a pair of large double 

 nerves, evidently corresponding with the two pair of an- 

 tennular nerves in ordinary crustaceans. The embryonic 

 condition of the whole supra-cesophageal portion of the 

 nervous system in the Lepadidae, corresponds with the 



