478 



SCIENCE 



[Vol. LV, No. 1427 



in New York City, has been appointed professor 

 of mining in Yale University to succeed Pro- 

 fessor James F. McClelland who resigned in 

 1919. 



At the New York Post-Graduate Medical 

 School and Hospital, the laboratory of patho- 

 logical chemistry, formerly a division of the de- 

 partment of laboratories, has been made an in- 

 dependent department and the name changed 

 to the department of biochemistry. The per- 

 sonnel consists of Victor C. Myers, Ph.D., pro- 

 fessor and director; Cameron V. Bailey, M.D., 

 and John A. Killian, Ph.D., assistant profes- 

 sors; Hilda M. CroU, M.A., associate and Her- 

 bert W. Schmitz, M.D., assistant. 



DISCUSSION AND CORRESPOND- 

 ENCE 

 THE FUTILITY OF THE HUMAN YOLK SAC 



In the current issue of the Anatomical 

 Record, Professor Arey publishes a brief but 

 very interesting contribution (No. 90) from the 

 Anatomical Laboratory of Northwestern Uni- 

 versity. He describes a human chorion con- 

 taining two embryos, of 11.5 and 12 mm. 

 respectively, one of which has a yolk sac, and 

 the other has none — that is, none was found, 

 and sections of the umbilical cord showed no 

 trace of a yolk stalk. Hence the broad con- 

 clusion is drawn that "the human yolk sac is a 

 vestige unessential to growth or differentia- 

 tion (including vasculogenesis)." It is stated 

 that one of these embryos "received all, or 

 essentially all, the cells destined to form a 

 yolk sac" and that "the total absence of a 

 yolk sac in one embryo, which is otherwise 

 normal in every way, further demonstrates 

 conclusively that this organ is not essential to 

 the growth of an embryo or to the proper dif- 

 ferentiation of its parts; indeed, the embryo 

 in question is slightly larger than its twin." 



Since from the days of Wolff the yolk sac 

 has been regarded as the source of the intes- 

 tinal tract, and in young human embryos is 

 seen to be the organ from which the allantoic 

 duet and the digestive tube proceed, the 

 startling nature of this conclusion becomes 

 apparent. But it is universally recognized 



that the yolk sac does its work in early stages, 

 and though the sac usually persists as a fune- 

 tionless rudiment until birth, its duct normally 

 becomes parted through atrophy in embryos 

 younger than the one under consideration. 

 Does Dr. Arey's case indicate anything more 

 than the precocious obliteration of the stalk of 

 an organ no less essential than the placenta, 

 likewise cast off after its very vital functions 

 have been performed? 



If the question is raised. Where then is the 

 yolk sac in Dr. Arey's case? his own studies 

 furnish a plausible answer, since in another 

 specimen he has described a single sac with 

 two stalks, each leading to a separate embryo. 

 Under such circumstances, the early oblitera- 

 tion of one of the stalks would give rise to the 

 conditions observed in the second case, and 

 this possibility must be eliminated before ac- 

 cepting the proposed conclusion. In reading 

 the account of a human embryo without a yolk 

 sac, we recall Bentham's incredulous comment, 

 "I am very glad, my dear sir, that you saw 

 that, for had I seen it myself, I wouldn't have 

 beReved it." 



Frederic T. Lewis 



Hakvaed Medical School, 

 Boston, Massachusetts 



DEFLECTION OF STREAMS BY EARTH 

 ROTATION 



The recent note by Professor Jennings sug- 

 gesting that the steeper vaUey sides on the 

 right of the south-flowing streams on Long 

 Island may be due in some manner to wind 

 action instead of to the deflective effect of the 

 earth's rotation is a welcome contribution to 

 an old problem. In spite of Gilbert's apparent 

 acceptance of the earth's rotation in explana- 

 tion of the unsymmetrical cross-section of those 

 valleys, the small size of their streams has 

 always stood in the way of it, all the more 

 since Bowman showed, on the basis of accurate 

 maps of the lower Mississippi, that even that 

 great river shifted its course to the east or left, 

 apparently under the control of the wind, and 

 not to the west or right, as it should if the 

 earth's rotation were in control.^ 



1 Science, XX, 1904, 273-277. 



