626 



SCIENCE. 



[N. S. Vol. XV. No. 381. 



NEW YORK ACADEMY OF SCIENCES. 

 SECTION OF BIOLOGY. 



At a regular meeting of the Section on 



March 10, the following program was offered: 



' The Four Pliyla of Titanotheres ' : Henry F. 



OSBOEN. 



' The Early DeveloiJment of Sharks from a 

 Comparative Standpoint': Bashford Dean. 



' The Cytologieal Phenomena of Maturation and 

 First Cleavage in the Cirriped Egg ' : Maurice 



A. BiGELOW. 



' The Effect of the Wind on Bird Migration ' : 

 C. C. Trowbridge. 



Professor Osborn presented some results re- 

 cently obtained for a U. S. Geological Sur- 

 vey Monograph. The Lower Oligocene Ti- 

 tanotheres prove to belong to four distinct 

 phyla, to which the prior generic names 

 Titanotherium, Symborodon, Megacerops and 

 Brontotherium may be applied. The chief 

 distinctions are found to be in the dolicho- 

 cephalic or brachycephalic form of the skull, 

 in the shape, length, position and mechanical 

 relations of the horns, and in the number and 

 form of the incisor and canine teeth. Each 

 genus obviously had distinctive modes of 

 fighting, locomotion and feeding. Titanothe- 

 rium extends from the base to the summit of 

 the Lower Oligocene. It is distinguished by 

 its long narrow skull, short horns, powerful 

 canines, vestigial incisors. Megacerops, on 

 the contrary, is broad-skulled, short-horned, 

 with obtuse canines, and with at least one 

 upper incisor. Symborodon is distinguished 

 by the narrowing of the anterior portion of 

 the premaxillaries, reduction of all the ante- 

 rior teeth, and by elongate horns placed im- 

 mediately over the eyes. In Brontotherium, 

 the horns are by far the largest and most 

 powerful, and acquire an extreme anterior 

 position, absorbing the free portion of the 

 nasals; all the upper cutting teeth persist; 

 great buccal plates are evolved; and the skull 

 measured along the base line is extremely 

 brachycephalic. The four types were illus- 

 trated by models and diagrams. 



Professor Bashford Dean considered briefly 

 some points in the development of sharks, and 

 attempted to reduce the type of the early de- 

 velopment of the recent types to that of their 



holoblastic ancestor. This form probably oc- 

 curred within the strict limits of the group 

 Elasmobranchii — for the absence of clasping 

 organs in the paleozoic genera of Acanthod- 

 ians and Oladoselachids predicates external 

 fertilization, and eggs many in number and 

 of small size. In the line of this comparison, 

 reference was made to the early development 

 of the Japanese 'pavement- toothed' shark, 

 Cestracion japonicus, in which, as the author 

 showed in a recent number of the 'Annota- 

 tiones Zoologicse,' surface furrows are present, 

 traversing the yolk, and are best interpretable 

 as reminiscent of holoblastic cleavage. In 

 the peculiar type of early development in 

 Chimmra, total cleavage is suppressed until 

 about the time of gastrulation, when cleavage 

 furrows appear in the region of the lower 

 pole and come to divide the egg into a number 

 of distinct blastomeres, only one mass of 

 which, however, become enclosed in the yolk- 

 sac of the embryo. The remaining blasto- 

 meres, by a process of continued division, pro- 

 vided nutriment for the embryo via gills and 

 gut. Dr. Dean announced the presence in 

 Chimmra of a true archenteric invagination, 

 occurring early and at some distance from the 

 margin of the blastoderm. It is small in size, 

 and has a distinct cellular floor. Its (an- 

 terior) dorsal wall was compared to the dorsal 

 lip of the archenteron of sharks, as described 

 by Eiickert and others. The ventral wall of 

 the archenteron of modern types of sharks 

 has thus lost its cellular character during the 

 process by which the embryo acquired a more 

 perfect and specialized (csenogenetic) mode 

 of obtaining nourishment from the yolk. 



The paper by Dr. Bigelow dealt chiefly with 

 protoplasmic movements and associated dis- 

 placements of the yolk materials in various 

 cirripede eggs during maturation and first 

 cleavage. The telolecithal distribution of the 

 egg substances, the formation and disappear- 

 ance of a yolk-lobe, and preeleavage move- 

 ments associated with differential distribution 

 of the entoblastic materials were described. 

 Finally, a turning of the first cleavage spindle 

 from a transverse to an oblique axis of the 

 ellipsoidal egg was compared with similar 

 more extensive movements in nematode eggs. 



