THE PALEONTOLOGIC RECORD 393 
It next resembles Obolella, then at a later stage it is like Schizocrania, 
and finally adult growth brings in the characters of Orbiculoidea. 
Raymond has shown the remarkable similarity of the neanic stage of 
Spirifer mucronatus to the adult S. crispus of the Niagara. Shimer 
and Grabau found in the upper Hamilton of Thedford, Ontario, a 
variety of Spirifer mucronatus that is very mucronate in the young 
and not at all so in the adult. The derivation of this form from 
S. mucronatus is beyond question. I have pointed out a precisely 
similar case in Platystrophia acutilirata var. senex. ‘This variety, 
which occurs in the upper Whitewater beds of Indiana and Ohio, has 
a hinge angle of nearly 90° in the adult. In the young, however, the 
outlines of the shell are exactly like the typical P. acutilirata, from 
which it is beyond any question descended. Greene has shown that 
Chonetes granulifer of the Carboniferous is, in the neanic stage, like 
the Devonian Chonetes, and that the hinge-spines come in at a consid- 
erably earlier stage in the Carboniferous than in the Devonian and 
Sulurian forms, showing the acceleration of this character. 
In the Bryozoa I have pointed out the fact that the colony behaves 
as an individual, and like an individual recapitulates in its ontogeny 
(astogeny) ancestral characters. This is beautifully shown in Fenes- 
tella, in which the earlier zoccia are strikingly like the adult zowcia of 
the Cyclostomata. The adolescent zoccia of Devonian Fenestella are 
similar to the adult zowcia of Niagara forms. Lang has brought 
together numerous cases of recapitulation among Jurassic and Creta- 
ceous Stomatopora and Proboscina. The method of dichotomy in the 
earlier portions of the colony is constantly more like the normal dichot- 
omy of ancestral species. 
In graptolites the remarkable researches of Ruedemann clearly 
indicate that the graptolite colony recapitulates ancestral characters, 
the proximal thece being similar to ancestral adult thece. He Says: 
The rhabdosomes in toto and their parts, the branches, seem also to pass 
through stages which suggest phylogenetically preceding forms. 
Among the trilobites the studies of Beecher, Walcott and Matthew 
are classic. Beecher has shown that there is a common larval form, 
the protaspis, and that in higher genera characters appear in the pro- 
taspis that are known only in the adults of more primitive genera. 
For example, the “ main features of the cephalon in the simple protaspis 
forms of Solenopleura, Liostracus and Ptychoparia are retained to 
maturity in such genera as Carausia and Acontheus.” Larval Sao has 
characters that occur in the adult of Ctenocephalus. The larval stages 
of Dalmanites and Proetus have characters that appear only in the adult 
of ancient genera. 
Among the corals Beecher and Girty show that such genera as 
Favosites have early stages that suggest Aulopora, Lang, in a recent 
