PALZZONTOGENY AND PHYLOGENY Rie, 
The available groups are the Brachiopoda, the Mollusca, and 
the Crustacea. 
Brachiopoda.—The brachiopods have this decided advantage, 
that they can be hatched in marine laboratories, and the various 
stages studied from the egg up, as has been done by Brooks, 
Kovalevski, Lacaze-Duthiers, Morse and Shipley, with the genera 
Cistella, Glottidia, Lacazella, Liothyrina, and Terebratulina. But it 
was reserved for the paleontologists Beecher, J. M. Clarke, and 
Schuchert to correlate the ontogeny of living forms with ances- 
tral genera and give a biogenetic classification of the Lrachiopoda* 
based on ontogenetic study. 
In living specimens the subdivisions of the embryonic stage, 
protembryo, mesembryo, neoembryo, and typembryo may easily 
be made out, but since these are shell-less the work of the pale- 
ontologist begins with the phylembryonic substage, when the shell 
gland secretes the protegulum. From this upwards the paleon- 
tologist works on equal terms with the zodlogist, for the suc- 
ceeding stages are capable of preservation, and may be compared 
with ancestral genera. Thus even the phylembryonic stage, or 
protegulum, is represented by the Cambrian genus Paterina, the 
ancestral prototype of all Lrachiopoda. 
Beecher and Schuchert? have also demonstrated that the 
Ancylobranchia (Terebratuloids) all go through a primitive Cen- 
tronelliform stage, and that the Helicopegmata (spire-bearers) do 
the same andare fora while genuine Ancylobranchta. Schuchert’s 
classification of the Brachiopoda, published in Eastman’s trans- 
lation of Zittel’s Text-Book of Paleontology, 1896, may be 
taken as strictly biogenetic so far as the data now at hand make 
such athing possible. And this is the only group of which we 
have a biogenetic classification. 
‘For correlation of stages of growth with generic changes, and for the literature on 
ontogeny and phylogeny of Brachiopoda, see papers by Dr. C. E. Beecher, Amer. Jour. 
Sci., Vol. XLIV, Aug. 1892, “ Development of Brachiopoda,” Part 2.; and Trans. 
Connecticut Acad. Sci., Vol. IX, March 1893, “Revision of the Families of Loop- 
bearing Brachiopoda;” and ‘“ The Development of Terebratalia Obsoleta Dall.” 
2Proc. Biol. Soc. Washington, Vol. VIII, July 13, 1893, ‘* Development of the 
Brachial Supports in Dielasma and Zygospira.” 
