390 APPENDIX. 



Plate IX. shows the fully developed and sexually mature 

 animals of the second generation from the mouth side, which, in 

 the natural position of Star-fishes (when creeping at the bottom 

 of the sea), in sea-stars (A 6) and sea-urchins (C 6), is below, 

 in sea-lUies (B 6) above, and in sea-cucumbers (D 6) in front. 

 In the centre we perceive, in all the four Star-fishes, the star- 

 shaped, five-pointed opening of the mouth. In sea-stars, from 

 each arm there extend several rows of little sucking feet, from 

 the centre of the under-side of each arm to the end. In sea- 

 lilies {B 6), each arm is split and feather-like from its base up- 

 ■\vards. In sea-urchins ((7 6) the five rows of sucking feet are 

 divided by broader fields of spines. In sea-cucumbers, lastly 

 (D 6), on the worm-like body it is sometimes only the five rows 

 of little feet, sometimes only the feathery tentacles surrounding 

 the mouth, from five to fifteen (in this case ten), that are exter- 

 nally visible. 



(Plates X. and XI. (Between pages 174 and 175, Vol. II.) 



Historical Development of the Crab-fish (Crustacea). — The two 

 plates illustrate the development of the different Crustacea from 

 the nauplius, their common primaeval form. On Plate XI. six 

 Crustacea, from six different orders, are represented in a fully 

 developed state, whereas on Plate X. the early nauplius stages are 

 given. From the essential agreement between the latter we may, 

 on the ground of the fundamental law of biogeny, with full 

 assurance maintain the derivation of the different Crustacea 

 from a single, common primary form, a long since extinct 

 Nauplius, as was first shown by Fritz Miiller in his excellent 

 work " Flir Darwin." " 



Plate X. represents the early nauplius stages from the ventral 

 side, so that the three pairs of legs, on the short, three- jointed 

 trunk are distinctly visible. The first of these pairs of legs is 

 simple and unsegmented, whereas the second and third pairs 

 are forked. All three pairs are furnished with stiff bristles, 

 which, through the paddling motion of the legs, serve as an 

 apparatus for swimming. In the centre of the body, the per- 



