474 



THE AMERICAN MUSEUM JOURNAL 



minute for several days. In other cases, 

 where several single heart-muscle cells are 

 unconnected, they will be seen to contract, 

 not sj'nchronously but the one independent 

 of the other. These interesting observations 

 rather indicate that the heart cells have an 

 inherent ability to contract and must so do 

 when placed in a favorable environment. 

 Rhythmic contraction is their function. 



In the developing embryo, these rhythmi- 

 cally contracting cells grow together, side by 

 side, end bj^ end, forming elongated muscle 

 fibers, which placed layer upon layer, even- 

 tually form the contractile portion of the cone- 

 shaped heart. Together with this growth 

 there develop nerve terminals, or ganglia, 

 and nerve fibers which connect the four- 

 chambered heart with the central nervous 

 system. This is essential for, although the 

 heart is capable of automatic rhythmic move- 

 ment due to the inherent property of the 

 muscle cells as we have already explained, it 

 is extremely important that this rhythmic 

 contraction should properly serve the needs 

 of its possessor. It is necessary that some 

 control should be exerted over its activities, 

 so that when the beat becomes slow, it should 

 be accelerated, and when too rapid, it should 

 be inhibited. These results are obtained by 

 two sets of nerve fibers coming from the cen- 

 tral nervous system. One set carries dimin- 

 ishing, or inhibiting, stimuli, the other aug- 



menting, or accelerating, stimuli. Because 

 the rate of the heartbeat changes quickly 

 in response to variations of internal and 

 external conditions, these regulatory nerves 

 are of the greatest value, for through their 

 agency, the motor power of the circulation 

 is quickly adjusted to suit the changing needs 

 of the organism and is adapted to changes in 

 the external environment. 



Single muscle cell from heart of an eight-days- in- 

 cubated chicken. When a section of the heart tissue 

 is planted in the blood plasma and placed in an in- 

 cubator, cells like above grow out from it, isolate 

 themselves, and begin to contract rhythmically 



Museum Notes 



Since the last issue of the Journal the 

 following persons have become members of 

 the Museum: 



Fellow, Mr. Charles Steele. 



Life Members, Mr. Gaylohd C. Hall and 

 Master Alexander Sanford Kellogg. 



Annual Members, Mrs. Robert C. Beal, 

 Mrs. Martin Burke, Mrs. John Peyton 

 Clark, Mrs. N. R. Norton, Mrs. Victor 

 M. Reichenberger, Mrs. Charles Ward 

 Sant)s, Misses Abby B. Bates, and M. M. 

 Rooney, Rev. John Addams Linn, and 

 Me.ssrs. E. Benjamin, John Evarts Clancy, 

 Benjamin Dorman, Royal P. Hamerschlag, 

 Robert S. Le.mmon, George McNeir, A. 

 Pagenstecher, Jr., and Morris Rippen- 

 bein. 



The Tillotherium is an animal belonging 

 to an extinct group of mammals whose re- 

 mains are found only in Eocene formations, 

 and although the American Museum's field 

 expeditions have searched these formations 

 for many years, never has any but the most 

 fragmentary material relating to this ani- 

 mal been found. This year, however, Mr. 

 Walter Granger, of the Museum's depart- 

 ment of vertebrate palaeontology, discovered 

 skulls, jaws, and probably all parts of the 

 skeleton, so that a reconstruction will soon 

 provide a means of establishing some valuable 

 relationships. 



The American Association for the Ad- 

 vancement of Science, which will meet in 



