ON THE FORMATION, SIGNIFICANCE AND CHEM- 
ISTRY OF THE WHITE AND YELLOW 
YOLK Or OVA 
OSCAR RIDDLE 
From the Laboratories of Zoélogy and Experimental Therapeutics, 
University of Chicago 
THREE PLATES AND ONE TEXT FIGURE 
NEN GTO GEC EL OLR 9. ee pes aoe chen ald f Loa-dia SSeS a teen Se ea 455 
A method of measuring the rate of growth of rapidly growing ova............ 457 
The rate of growth of the cvum of the common fowl......................... 458 
iteelarce ova more thansO.0) mime Ghimeter ss. 240-2). 06 ee eee 458 
Pee smalleovanlessimansorOMmm: in diameter. sa... eas ci ee ee 459 
The thickness of the strata of white and yellow yolk in the egg of the common 
Ong Spee eoele pes Se ce Se a a ee ae et RU rect AIS So lene eS 2: c 461 
The coincidence of the amount of yolk deposited in a day, with the amount 
of yolk contained in a layer of white and yellow yolk...................... 462 
Yolk stratification in eggs of other animals as seen in the light of its causation 
iho oeKoep eG omee Pe Ne sibs. 5 6 She. chs a. Pe 462 
Onsinechemistinyotwwoitesandryellow yolke a2 5: 35s atee ener enya 467 
On the mechanism of yolk formation and de-formation.....................- 470 
1. The part played by the reversible action of enzymes.................. 471 
2. Therdle of the partition coefficient of the elements of yolk ............. 475 
3. These two factors and the histological data ...................h.ceeus- 477 
SUTEUTICER ES emt ts eNO is ce ona 5 Résces tno py + ne ooh Se op ne ee ee 482 
MGiteraturencibedre teary Ses oi ob soc see wl Shea 2 Ree DOO eIc ORE ICrae 485 
INTRODUCTION 
Very many thousands of pages have been written concerning 
yolk—its presence, formation, varieties and distribution in eggs. 
Indeed, the task of recording such a series of facts has been 
repeated on nearly every egg that has come under the closer ob- 
servation of the biologist; while some eggs, notably those of the 
frog and the fowl,-have submitted their yolks to the observa- 
tion and description of dozens of different investigators. Not- 
JOURNAL OF MORPHOLOGY, VOL. 22, NO. 2 
455 
