50 Traces of Unity in the Appendicular 



before the other, the hindermost carrying a moveable, 

 large, elytra-like scale, the foremost serving as a base 

 for a single, moveable, many-jointed, tapering, antenna. 

 There is a bifid arrangement in the basal portion in 

 each case which is evidently a shadow of the double- 

 foot of the isopod and branchiopod crustaceans and of 

 many of the annulata ; and there can be little doubt 

 that the antennae are modifications of the palps which 

 occupy the corresponding situation in many other 

 crustaceans, and that the basal portion below the 

 antennas agrees in like manner with the parts corre- 

 sponding to them in the more ordinary feet. Nor is a 

 different conclusion to be drawn from the more excep- 

 tional forms which the antennae take in other inverte- 

 brate creatures. In the spider, for example, the fact 

 that the antenna is confounded with the mandible, is 

 only another proof of the common nature of the antenna 

 and the mandible : and what other conclusion is to be 

 drawn from the similarity of the eye-less and the eye- 

 bearing " horns " of the gasteropod except this, that the 

 eye-less horns, which are the homologues of the 

 antennae, and the eye-bearing horns are radically con- 

 natural ? In short, it would not be difficult to show 

 that the antennae may take upon themselves the form 

 and office of the limbs which have to do the work of 

 prehension and locomotion, or that they may even 

 become transformed into root-like processes. The larval 

 barnacle (Lepas), for example, is provided, not only 

 with pedunculated eyes, but with long antennae which 

 may be used in creeping and holding, as well as in 

 feeling, but the adult creature is both blind and palp- 

 less, the eyes having disappeared in the course of 

 moulting, and, contemporaneously with this change, the 

 palps or antennae having become transformed into the 



