THE DEVELOPMENT OF THE ALBINO RAT, 
MUS NORVEGICUS ALBINUS 
I. FROM THE PRONUCLEAR STAGE TO THE STAGE OF MESO- 
DERM ANLAGE;, END OF THE FIRST TO THE END 
OF THE NINTH DAY 
G. CARL HUBER 
From the Department of Anatomy, University of Michigan, and the Division of 
Embryology, Wistar Institute of Anatomy and Biology, Philadelphia 
THIRTY-TWO FIGURES 
LTO IOV So BO Ae eee uci ats eS ote cra tot a a Pn SPREE BA ES 2 ay 247 
RUE OLA ANOS UMO GIS. ccc k ee A Shieh te kd hee iw oelere'es oS cehes DHOE A Laer eee 249) 
OvMlaniomematiration, and tertilivatiOn.......00-.+.2.:o.+scee os oe eee 253 
PeeTEIE ARES RNs 2 AM Pe ok thee oc S gna o's OE ono a uaa eee 257 
PERMA ee UO MNASELS CH. tye (tare ans = cases spstetees His da. o'd's see © Sule dana eA ORS 265 
BARBI SEES SS ona win An i a AN Ce SO) ke 265 
Am C CBS S CMA ener ats eRe ae OE ee ld aun nS wis 6 Sno Se ee 273 
IC CMIMSI ARE Certs heron Sa NAR Or Ss th tal ate CR ae eee 275 
URLOmIO=Cellyst ayer ne esen gsr state f staystsieises. <b <te aie Skee Lees | ok eee 279 
Summary of segmentation stages, rate, and volume changes................ 280 
Completion of segmentation and blastodermic vesicle Sanmanioe eee peithS 286 
Blastodermic vesicle, blastocyst, or germ vesicle.......................0,0- 300 
Late stages of blastodermic vesicle, beginning of entypy of germ layers. ... 307 
Development and differentiation of the egg-cylinder....................... 317 
Late stages in egg-cylinder differentiation, and the anlage of the mesoderm 336 
we STLCTE CER 0 AE oe oer ergy ee le A ae rene ets tS tert 352 
SRR MAIR CECI PT En te ee SRE NY ie Sa oa 5. an wd 9 ached 6 ae ee eek 356 
INTRODUCTION 
The early developmental stages of placental mammals, em- 
bracing the stages of sex cell maturation and fertilization, of 
segmentation, of blastodermic vesicle and germ layer forma- 
tion, though subject of numerous contributions extending over 
many years, have in no form been completely investigated. The 
literature dealing with the phenomena of maturation and fer- 
247 
JOURNAL OF MORPHOLOGY, VOL. 26, NO. 2 
