DEVELOPMENT OF THE ALBINO RAT 261 
living rat ova Long found that the constriction of the second 
polar body may be completed three-fourths of an hour after 
its inception, then it must be evident that the pronuclear stage 
extends through a period which exceeds 10 to 12 hours, since in 
none of my pronuclear stages obtained 24 hours after insemina- 
tion was evidence of first segmentation spindle observed. 
In order to determine accurately the relative position of the 
ova within the oviduct during the pronuclear stage and the 
stages of segmentation, oviducts containing ova were recon- 
structed after the Born wax plate method. In form, relations, 
and general structure, the oviduct of the albino rat is essen- 
tially the same as that of the mouse as described by Sobotta. The 
oviduct of the rat measures from fimbriated end to termination 
in the uterine horn from 2.5 ecm. to about 3.0 cm. It presents 
eight to ten fairly constant major folds, the middle group of 
which is closely applied to the ovarian capsule. The upper or 
distal folds pierce the capsule, ending in the fimbriated end 
found within the capsule, while the lower or proximal folds, 
proximal with reference to the uterine horn, effect connection 
with the uterine horn. These relations are essentially the same 
as those described by Sobotta for the oviduct of the mouse. This 
observer recognizes four segments in the oviduct of the mouse, 
characterized by epithelial lining, nature and extent of folding 
of the mucosa, and thickness of the musculature. The first 
segment, which falls to the infundibulum, presents a thin muscu- 
lature and high mucosal folds with epithelial lining consisting 
of relatively short cylindrical cells with distinct cuticular border 
and long cilia. As characteristic of this portion of the tube 
there are further described accessory nuclei compressed between 
the epithelial cells. Only this portion of the oviduct is ciliated. 
In the second segment, the lumen is large and the folds of the 
mucosa prominent. They are covered by a non-ciliated epithe- 
lium, without distinct cuticular border. The musculature is 
relatively thin. In the third segment the musculature is well 
developed with circularly and longitudinally disposed cells. The 
lumen is narrow and the folds are nearly absent, while the epithe- 
lium is of a simple columnar variety. The fourth segment, not 
so well characterized, consists of the loops which make con- 
