EMBKYOGENY 



205 



(a) A few examples will make this more compre- 

 hensible. On driftwood and sunken piles there is often 

 found a mussel-like animal attached by a stalk 

 the Barnacle (Lepas anatifera, L.) (Fig. 39). Formerly 

 they were regarded as mussels, although even on a 

 superficial examination much is perceived which is 

 not exactly mussel-like, as for instance the possession 

 of numerous movable limbs, the clasping feet (Ran- 

 kenfiisze). 



The most remarkable thing is that from the eggs 

 of this animal crab larvae issue of the so-called ' Naup- 

 lius ' type. The Nauplius larva is an embryonic stage 

 common to all the lower crabs (Entomostraca). After 

 a definite time the larva attaches itself by its own ten- 

 tacles to a support, lime is deposited in the shell, 

 the head becomes a stalk, the eye is aborted, the swim- 

 ming feet become clinging feet (which serve to whirl 

 food within reach but not for locomotion), and the 

 Barnacle is complete. 1 On close examination we see 

 certainly also, in the adult form, still other true crab- 

 like characters, as for instance in the construction 

 of the mouth, the nervous system, the legs, etc. In 

 short there remains everything of a crab type : in the 

 first place the embryogeny up to that stage where such 

 constructions were added, the positive adaptations to the 

 sessile mode of life, and furthermore all the characters 

 of the Cirripedia, which also can be of service in their 

 old form in the new mode of life jaws, nerve system, 

 and make of the legs. In other cases certainly it is 



1 Heffe : Abstammungslehre und Darwinismus, p. 30. 



