PHYLOGENY. 87 



organism whose environment and habits of life were 

 essentially like those of the modern Appendicularia.' 

 Appendicularia is well known as the tunicate which 

 retains throughout life, the notochord and tail which 

 characterize the larvae of other Tunicata. 



Omitting from consideration the two classes above 

 mentioned (Acrania and Tunicata), whose remains 

 have not yet been certainly found in a fossil state, there 

 remain the following : the Pisces, Batrachia, Mono- 

 condylia, and Mammalia. 1 



I have traced the origin 2 of the Mammalia to the 

 theromorous reptiles of the Permian epoch, and these 

 to the Cotylosauria. The latter include the Pelycosau- 

 ria, Procolophonina, Anomodontia, and perhaps other 

 orders. In the Cotylosauria the temporal region is 

 roofed over, which roof is reduced in the Pelycosauria 

 to one postorbital arch of the skull, and this is the zy- 

 gomatic of the Mammalia. In both Reptilia and Mam- 

 malia (excepting Prototheria and Procolophonina 3 ) the 

 coracoid element is of reduced size, and is co-ossified 

 with the scapula. In both (except Cotylosauria) the 

 capitular articulation of the ribs is intercentral. In 

 both the humerus has distal condyles and epicondyles, 

 and there is an entepicondylar foramen in the Pelyco- 

 sauria as in the lower Mammalia. The posterior foot 



ISee The Evolution of the Vertebrata Progressive and Retrogressive ; Amer. 

 Naturalist, 1885. Dohrn, Der Urspriing der Wirbelthiere ztnd das Princip 

 des Functionwechsels, Leipsic, 1875. " On the Phylogeny of the Vertebrata," 

 Cope, American Naturalist, Dec., 1884. See also the following references: 

 American Naturalist, 1884, p. 1136 ; Proceedings of the Academy of Philadelphia, 

 1867, p. 234 ; Proceedings American Philosophical Society, 1884, p. 585 ; American 

 Naturalist, 1884, p. 27; Proceedings American Association for the Advancement 

 of Science, XIX, 1871, p. 233 ; Proceedings American Philosophical Society, 1882, p. 

 447; American Naturalist, 1884, pp. 261 and 1121 ; Report U. S. Geol. Survey W. 

 of tooth Mer., G. M. Wheeler, 1877, IV, 2, p. 282. 



2 Proceedings American Philosophical Society, 1884, p. 43. 



3 Seeley, Philos, Trans. Royal Society, 1889, 269. 



