76 THE DOCTRINE OF DESCENT. 
Turrilites, Scaphites, Baculites, and others are considered. 
The prime of the great sea-lizards is also past, but the 
marshes of the Wealden period harboured new forms 
of colossal land-lizards. The long-tailed cray-fishes are 
joined by the true crabs, the most highly developed 
forms of the class. In the Oolite and Chalk also occur 
the chief of the sea-urchin-like Echinoderms. As yet we 
have not mentioned the class of Echinodermata, in order 
that we might here point out in conjunction several of 
the more important phases of their geological occurrence. 
Desor,* a distinguished judge of this class, has lately 
examined how in this large group of Echinz the pro- 
gress of organization is gradually manifested, on which 
occasion he was induced to make some general reflec- 
tions on the principle of progression, as applied to 
the Echinoderms, probably known to all our readers in 
their representatives the star-fish and sea-urchins. If 
articulate, as well as vertebrate, animals attain a higher 
grade of development by the differentiation of the con- 
secutive segments of the body, the superior unity, and 
therewith higher perfection, of the Echinoderm’s body 
is evinced when the spines, or so-called antimera, give 
way to the unity of the whole. 
The more distinct these elements are, that is to say, the 
more independent they remain, the lower is, not only the 
articulate animal, but also the Echinoderm. Accord- 
ingly, the star-fish, and to some extent the feather-stars, 
stone-lilies, or crinoids, occupy the lowest rank. But 
here, unluckily, paleontological tradition likewise aban- 
dons us. Only so much is certain, that in the older 
fossiliferous strata both divisions are abundantly repre- 
* Bulletin de la Société des Sciences Naturelles de Neufchitel, IX 2. 
