238 FOOT-NOTES TO EVOLUTION. 



Brachiopoda. The brachiopods have this decided 

 advantage, that they can be hatched in marine labora- 

 tories, and the various stages studied from the egg up, 

 as has been done by Brooks, Kovalevski, Lacaze-Du- 

 thiers, Morse, and Shipley, with the genera Cistella, Glot- 

 ttdia, Lacazella, Liothyrina, and Terebratulina. But it 

 was reserved for the paleontologists Beecher, J. M. 

 Clarke, and Schuchert to correlate the ontogeny of liv- 

 ing forms with ancestral genera, and give a biogenetic 

 classification of the Brachiopoda * based on ontogenetic 

 study. 



In living specimens the subdivisions of the embryonic 

 stage, protembryo, mesembryo, neoembryo, and typem- 

 bryo may easily be made out, but since these are shell- 

 less the work of the paleontologist begins with the phyl- 

 embryonic substage, when the shell gland secretes the 

 protegulum. From this upward the paleontologist 

 works on equal terms with the zoologist, for the suc- 

 ceeding stages are capable of preservation, and may be 

 compared with ancestral genera. Beecher and Schu- 

 chert f have demonstrated that the Ancylobranchia (Tere- 

 bratuloids) all go through a primitive Centronelliform 

 stage, and that the Helicopegmata (spire-bearers) do the 

 same, and are for a while genuine Ancylobranchia. Schu- 

 chert's classification of the Brachiopoda, published in 

 Eastman's translation of Zittel's Text-Book of Paleontol- 



* 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, Au- 

 gust, 1892, Development of Brachiopoda, Part II ; and Trans. 

 Connecticut Acad. Sci., vol. ix, March, 1893, Revision of the 

 Families of Loop-bearing Brachiopoda ; and The Development 

 of Terebratalia Obsoleta Dall. 



f Proc. Biol. Soc. Washington, vol. viii, July 13, 1893. Devel- 

 opment of the Brachial Supports in Dielasma and Zygospira. 



