148 METAMORPHOSES OF ANIMALS. 



comes a more and more perfect animal, whilst the worm 

 remains in its inferior state. 



380. Similar instances are furnished by animals belong- 

 ing to all the types of the Animal Kingdom. Who would 

 think, at the first glance, that a Barnacle or an Anatifa were 

 more nearly allied to the crabs than to the oyster ? And, 

 nevertheless, we have seen (372), in tracing back the Anat- 

 ifa to its early stages, that it then bears a near resemblance 

 to a little Crustacean (Fig. 148, d). It is only when full 

 grown that it assumes its peculiar mollusk-like covering. 



381. Among the Cuttle-fishes there are several, the 

 Loligo (Fig. 47) for example, which are characterized by 

 the form of their tentacles, the two interior being much 

 longer than the others, and of a different form ; whilst 

 in others, as the Octopus, they are all equal. But if we com- 

 pare the young, we find that in both animals the tentacles 

 are all equal, though they differ in number. The inequality 

 in the tentacles is the result of a further development. 



382. Among the Radiata, the Pentacrinus and the Comat- 

 ula exemplify the same point. The two are very different 

 when full grown, the latter being a free-swimming star-fish 

 (Fig. 151), while the former is attached to the soil, like a 

 Polyp. But we have seen (377) that the same is the case 

 with Comatula in its early period ; and that in consequence 

 of a further metamorphosis, it becomes disengaged from its 

 stem, and floats freely in the water. 



383. In the type of Vertebrates, the considerations drawn 

 from metamorphoses acquire still greater importance in re- 

 ference to classification. The Sturgeon and the White-fish 

 before mentioned (306) are two very different fishes ; yet, 

 taking into consideration their external form and bearing 

 merely, it might be questioned which of the two should 

 take the highest rank ; whereas, the doubt is very easily 

 resolved by an examination of their anatomical structure. 



