48 LEPADID.E. 



nerves to the fifth and sixth pair of cirri ; it is clearly 

 formed by the union of the fifth, with what ought to have 

 formed a sixth ganglion. The two nerves going to the 

 sixth cirrus give off on their inner sides, each a great 

 branch to the penis. In Pollicipes mitetta, in which 

 there are only four instead of five thoracic ganglia, it is 

 evident from the outline and position of the nerves going 

 to the fourth pair of cirri, that the fourth ganglion is 

 fused into the fifth, itself, as we have just seen, nor- 

 mally composed of two consecutive ganglia. In this 

 Pollicipes there is other evidence of concentration in 

 the nervous system, for none of the ganglia show signs 

 of being formed of lateral pairs; the second is close to 

 the first ; and the abdominal double chord is in part 

 separated by a mere cleft ; lastly, as we shall immedi- 

 ately see, the same remark is applicable to the supra- 

 cesophageal ganglia. 



The latter (d) alone remain to be described ; they 

 present far more diversity in shape than do the thoracic 

 ganglia; they are almost always seen in outline to be 

 laterally distinct, and usually resemble two pears with 

 their tapering ends cut off and united ; in a transverse 

 line they are as long as the infra- oesophageal ganglion, 

 but are much less massive. In Lepas fascicularis (d), 

 they are pear-shaped; in Pollicipes mitella they are 

 globular, and separated by a third globular ganglion, 

 which I believe is the ophthalmic ganglion, presently 

 to be described; in Pollicipes spinosus, however, the 

 ophthalmic ganglion is, as usual, placed in advance of 

 the supra-cesophageal ganglion, which latter, in this one 

 species, shows no sign of being formed of a lateral pair 

 fused together. In Alepas cornuta the supra-cesophageal 

 ganglion consists of two quite distinct ganglia, elongated 

 in the longitudinal axis of the body, and separated from 

 each other by the whole width of the mouth ; the chord 

 which unites them is of the same thickness as the rest of 

 the collar. In all the genera, from the front of each 

 of the two supra-cesophageal ganglia, a pair of nerves, 



