226 



SCIENCE. 



[N. S. Vol. VII. No. 164. 



divides symmetrically, always (Discooselis'!) , 

 or occasionally {Leptoplana) . This cell is 

 probably to be regarded as the prototype of 

 tlie second somatoblast of annelids and 

 moUusks, which divides symmetrically to 

 form the 'primary mesoblasts,' the meso- 

 blast bands (ento-mesoblast) being a new 

 formation and the ecto-mesoblast (' larval 

 mesenchyme,' etc.) being homologous with 

 the mesoblast of the polyclades. This inter- 

 pretation is sustained by the fact that the 

 posterior cell of the fourth quartet may con- 

 tain entoblastic elements largely developed 

 (CrepicZitZa), considerably reduced {Nereis) 

 or reduced to a pair of rudimentary or ves- 

 tigial cells {Aricia, Spio). The latter strik- 

 ingly illustrate ancestral reminiscence in 

 cell-lineage, and represent the penultimate 

 stage in a series which begins with the 

 polyclade. These facts and others were 

 urged in support of the cell theory of devel- 

 ment and the value of cell-lineage in the 

 investigation of homologies. 



The Characters and Phylogeny of the Ambly- 



poda. H. F. OsBOBN. 



As a result of the recent explorations by 

 the American Museum of Natural History, 

 a complete skeleton of Coryphodon has been 

 procured and mounted, as well as a nearly 

 complete skeleton of Pantolambda, not only 

 one of the oldest geological, but the most 

 archaic type of ungulate, from a mor- 

 phological standpoint, hitherto discovered. 

 The restoration of this animal shows it was 

 completely plantigrade, progressing upon 

 the plantar and palmar surfaces of the feet, 

 like a bear. There is an os-centrale carpi 

 as in the Creodonta, and the whole skeleton, 

 is strongly impressed with the Creodont 

 type, reinforcing the evidence already 

 derived from the Phenacodontidje, that the 

 Ungulata sprang from Unguiculate animals. 

 This restoration agrees with a prior restora- 

 tion of Periptychus, and the resemblances 

 between these two skeletons are very 



marked, supporting the author's views ex- 

 pressed in 1893, that Periptydms should be 

 placed among the Amblypoda. This gives 

 this very ancient order of ungulates a very 

 wide functional variation from small arbo- 

 real types to the huge Uintatheres of the 

 Eocene. The evolution of the skull can 

 now be fully traced out, and in Coryphodon 

 we observe the rudiments of the frontal and 

 parietal horns of Uintatherium. 



A Series of Specimens Illustrating the Develop- 

 ment of the Chick. Mrs. S. P. Gage. 

 These illustrate Professor Gage's idea 

 that in an embrj'ological series for a mu- 

 seum all stages sufficiently different to be 

 easilj' recognized by the naked eye are to 

 be included, to the adult condition. Thej^ 

 are the unincubated germ, the 12, 18, 24, 

 36, 48, 60, 72 and 96-hour chick; and from 

 this point on to hatching are at intervals of 

 one day, ending with a chick just emerging 

 from the shell at the 21st day. Mounted 

 skins of chicks 24 hours and six days after 

 hatching, of one in the stage known com- 

 mercially as a broiler and of a hen and 

 rooster complete the series. 



All the specimens were fixed in 10 per 

 cent, nitric acid, washed to free from yolk 

 and preserved in alcohol. From the 7th 

 day on, the membranes were too extensive 

 to show both them and the chick, and par- 

 allel series were arranged in the same jar, 

 one to exhibit the chick and one the mem- 

 branes. 



The earlier stages were mounted on cover 

 glasses, which had been albumenized and 

 built up in a slightly convex form with 

 collodion and brushed with a coating of 

 collodion containing lamp black. The germ 

 was floated on to the cover under alcohol 

 and fixed in place by thin collodion. Glass 

 strips to fit the jars were prepared by al- 

 bumenizing and (unless the glass were 

 black) coating with thin collodion contain- 

 ing lamp black, thus giving a strongly con- 



