6626 Crustacea. 



youngest stage of development as in its complete form. The eye in 

 the larva of a crab appears by far the most important organ that it 

 possesses, being considerably larger in relation to the animal than in 

 the full-grown crab. 



I have not ascertained the circumstance in the pedunculated orders, 

 but it is a fact in relation to the sessile-eyed Crustacea that the organ 

 continues to grow, that is, the number of lenses in the visual organs 

 continually increases with age, and that a considerable number is 

 present to build up one eye ; in the young amphipod there are from 

 eight to twelve, in the adult there may be from fifty to sixty ; but in 

 the crabs and lobsters there are a great many more ; the quantity 

 being required to counteract the want of more perfect movement and 

 the position of the organ. 



It was on this class of animals that Divine Will first manifested his 

 power, in the construction of these organs ; and though ages, which 

 the mind wearies in attempting to calculate, have since passed away, 

 the plan of the organ is still the same ; it differs not more than spe- 

 cifically from that of recent Crustacea. It evidently, in the Trilobites, 

 from its position, belonged to an animal that was always groping at 

 the bottom of the sea, for its vision was limited to things that were 

 situated above it ; and that it frequented shallow water is also 

 demonstrable, from the limited extent of its upward range. In the 

 pedunculated order of recent Crustacea the range of vision is more 

 extended, and is also rendered more complete from the fact that the 

 organ is raised upon foot-stalks and moveable ; but still the power 

 of vision appears most complete in the centre of the organ. Upon 

 the inner surface of the eyes there are no lenses placed ; thus all 

 objects between them are less distinctly seen. To overcome this 

 circumstance as much as possible, and also to keep guard more 

 watchfully, the eyes are as in the timid hare, keeping especial look- 

 out behind. The common shrimp has often allowed the hand to 

 come quite close to it, when the action is made in front, before it 

 observed the circumstance; but will dart away long before if an 

 attempt be made to steal near it from any other quarter. In com- 

 paring the present with the past, the most recent with the most 

 ancient, there appears no change of purpose ; the organ that was 

 found to be adapted for the primeval waters is equally available for 

 the ocean of the present day ; the first-created eye and the last are 

 alike complete and perfect in their adaptation to the class of animals 

 to which they belonged, even though it may bear, as the Trilobite to 

 the recent Crustacea, in general structure, the most distant analogy 



