S 2 



THE DARWINIAN THEORY 



processes penetrating the crab's skin and spreading 

 out in its body, from which they absorb the nutri- 

 ment on which the parasite lives and grows. 



Yet when we turn to the development of these 

 animals, we find that, utterly unlike as the adult 



Fig. io. 

 A B C 



Stages in the Development of the Barnacle (Balanus). 



A, Nauplins stage; B, Second stage, in which the first pair of 

 swimming appendages of the Xauplius are converted into antenna; and the 

 rudiments of the six pairs of cirri appear; C, Pupa stage— in this stage 

 the animal is free-swimming and has six pairs of legs, antennules, two large 

 compound eyes, and imperfectly developed masticatory appendages. The 

 pupa becomes attached by its antennules and develops into D, the adult 

 Barnacle. E, Group of Barnacle shells. 



forms are, the young of all three genera hatch in the 

 form known as a Natiplius. This Nauplius larva 

 has a short unsegmented body, three pairs of 

 appendages, used for locomotion, and a single median 

 eye; and although the Nauplii are not identical one 

 with another, yet they agree very closely in all 



