THE PALEONTOLOGIC RECORD 3 °3 



It next resembles Obolella, then at a later stage it is like Schizomania, 

 and finally adult growth brings in the characters of Orbiculoidea. 

 Raymond has shown the remarkable similarity of the neanic stage of 

 Spirifer mueronatus to the adult S. crispus of the Niagara. Shinier 

 and Grabau found in the upper Hamilton of Thedford, Ontario, a 

 variety of Spirifer mueronatus that is very mucronate in the young 

 and not at all so in the adult. The derivation of this form from 

 S. mueronatus 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 

 Silurian 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 zooecia are strikingly like the adult zocecia of 

 the Cyclostomata. The adolescent zocecia of Devonian Fenestella are 

 similar to the adult zocecia 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 thecse being similar to ancestral adult thecas. 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 



