DEVELOPMENT AND EMBRTOLOOT. 459 



organization being higher or lower. But no one probably 

 will dispute that the butterfly is higher than the cater- 

 pillar. _ In some cases, however, the mature animal must 

 be considered as lower in the scale than the larva, as with 

 certain parasitic crustaceans. To refer once again to cirri- 

 pedes: the larvae in the first stage have three pairs of loco- 

 motive organs, a simple single eye, and a probosciformed 

 mouth, with which they feed largely, for they increase 

 much in size. In the second stage, answering to the 

 chrysalis stage of butterflies, they have six pairs of beauti- 

 fully constructed natatory legs, a pair of magnificent com- 

 pound eyes, and extremely complex antennse; but they 

 have a closed and imperfect mouth, and cannot feed: their 

 function at this stage is, to search out by their well-devel- 

 oped organs of sense, and to reach by their active powers 

 of swimming, a proper place on which to become attached 

 and to undergo their final metamorphosis. When this is 

 completed they are fixed for life: their legs are now con- 

 verted into prehensile organs; they again obtain a well- 

 constructed mouth; but they have no antennae, and their 

 two eyes are now reconverted into a minute, single, simple 

 eye-spot. In this last and complete state, cirripedes may 

 be considered as either more highly or more lowly organized 

 than they were in the larval condition. But in some genera 

 the larvae become developed into hermaphodites having 

 the ordinary structure, and into what I have called com- 

 plemental males; and in the latter the development has 

 assuredly been retrograde, for the male is a mere sack, 

 which lives for a short time and is destitute of mouth, 

 stomach, and every other organ of importance, excepting 

 those for reproduction. 



We are so much accustomed to see a difference in struc- 

 ture between the embryo and the adult, that we are tempted 

 to look at this difference as in some necessary manner 

 contingent on growth. But there is no reason why, for 

 instance, the wing of a bat, or the fin of a porpoise, should 

 not have been sketched out with all their parts in proper 

 proportion, as soon as any part became visible. In some 

 whole groups of animals and in certain members of other 

 groups this is the case, and the embryo does not at any 

 period differ widely from the adult: thus Owen has re- 

 marked in regard to cuttle-fish, "there is no metamor- 



