Crustacea. 



6629 



of the several lenses would greatly perfect the adaptation of the organ 

 to the medium in which it exists. We may therefore fairly infer that, 

 in common with the universal scheme in nature, the organ is as 

 fully adapted to see objects distinctly in the water as other animals 

 see things on land ; and thus, to all, the endowment is made a 

 blessing. Diviue love has ruled this a paramount law, and nowhere 

 do we see it more forcibly exemplified than in the organs of vision of 

 the Cirripodia. Whilst they are young, and swim freely in the water 

 in the full light of day, and have to seek out and choose their own 

 permanent place of rest, they have distinct eyes, although in the 

 earliest form the two are confluent, and appear as a single organ. In 

 a second stage they increase in size, and separate ; but directly the 

 animal is fixed to the rock, and shut up in his shellj r cavern, the 

 organs are not to be seen, and eyes, really as such, probably do not 

 exist, although careful dissection first demonstrated, by Prof. Leidy, 

 in the Balanus, or sessile group of barnacles, and since by Mr. Darwin 

 in Lepadidae, or pedunculated family of these same Crustacea, that 

 the ophthalmic ganglion is present in the adult form. Thus the 

 animals appear to be endowed with a low power of vision, which 

 probably does not reach beyond the consciousness of objects that 

 may interfere with the rays of light that pass into the shelly entrance. 



We have repeatedly noticed them throwing their cirri with the 

 unerring constancy of clock-work, until a hand be moved in front of 

 their small opening, when they immediately retract themselves, and 

 shut up their valves until the supposed danger has passed away ; but 

 beyond this, sight can be of no use to them. No animal but man is 

 supposed to enjoy the beautiful in nature; sight, therefore, is only 

 valuable to animals to seek food and avoid danger, and it is only in the 

 latter sense that it can be available to the barnacles in their adult 

 character, since they are anchored to a rock and have no power to 

 move. 



But the barnacle family are not the only Crustacea in which the 

 organs of vision are reduced to a rudimentary condition. Some of 

 the parasitic Isopods take up their abode beneath the carapax of the 

 higher forms, where they become a disease, and distort the fair pro- 

 portions of the creature upon whose life they feed. The females of 

 Bopyrus and allied genera are found upon crabs, shrimps and bar- 

 nacles, where they feed and vegetate to such an extent that they 

 outgrow all resemblance to the normal character of a Crustacean; 

 whereas the male, which continues through life an active individual, 

 preserves the typical form. 



