DISTRIBUTION OF MITOCHONDRIA IN THE PLACENTA. 107 



locking folds. The cells of the chorion vary in height in different parts of each fold; 

 at the apices of the chorionic folds they are of low columnar form, on the sides of 

 the folds they are cuboidal, while in the depths of the folds a transition again occurs 

 to columnar cells 20 to 30 M i n height. Situated in the basal half of each cell is a 

 single large, oval nucleus which takes the green faintly, has a well-defined chromatin 

 network, and one or two large fuchsinophilic nucleoli. The protoplasm of the basal 

 half of the cell also stains a faint green. In the apical zone the protoplasm is clear 

 and unstained. In many cells it is extensively vacuolated and degenerated cells 

 with pycnotic nuclei and diffusely fuchsinophilic protoplasm are common. In a 

 number of the chorionic epithelial cells a fuchsinophilic, colloid-like substance is 

 found in the basal zone (usually between the nucleus and the base of the cell), 

 varying in amount from one or two small granules to large masses 5 to 6 ^ in 

 diameter. The larger masses are surrounded by a clear zone as though they had 

 contracted during fixation. The cdls containing this colloid substance present 

 no evidence of degeneration. 



The mitochondria are concentrated in the apical half of the cells facing the 

 uterine mucosa (fig. 1). They are quite abundant in the apical zone and appear 

 as minute granules and very delicate, slightly curved rods. The rods and rows of 

 granules are parallel to the long axis of the cell and appear as though streaming 

 from its apex towards the nucleus. They steadily decrease in number as the 

 distance from the apex increases, and it is rare to find any in the region of the 

 nucleus and none is seen in the zone between the nucleus and the base of the cell. 

 The cuboidal and low columnar cells of the sides and apices of the folds are similar 

 to the high columnar cells in the depths of the folds, except that the various regions 

 of the cell are less well marked and fewer cells contain colloid droplets. 



The chorionic epithelium rests on a very thin basement membrane which is 

 supported by a delicate connective-tissue layer containing the smaller fetal blood- 

 vessels. This layer is composed of small spindle or stellate cells which do not 

 differ from fibroblasts found in other tissues. They contain a few minute granular 

 and rod-shaped mitochondria. The endothelium of the fetal vessels also contains a 

 few granular and rod-like mitochondria and herein does not differ from ordinary 

 vascular endothelium. This delicate connective-tissue layer merges into a thin 

 layer of coarser fibrous tissue which contains the larger fetal blood-vessels, the cells 

 of which are larger than those of the preceding one and contain larger and more 

 abundant mitochondria. This fibrous layer is covered by the allantoic mem- 

 brane, which is composed of a single layer of flattened epithelial cells resting on a 

 delicate basement membrane. The allantoic epithelium is quite rich in minute 

 granular mitochondria which are scattered uniformly through the protoplasm. 



The uterine mucosa facing the chorionic epithelium is composed of a single 

 layer of low cuboidal cells resting on a basement membrane. Each cell contains a 

 single relatively large, round or oval nucleus which stains deep green and contains 

 one or two large fuchsinophilic nucleoli. The protoplasm stains lightly with green 

 and contains an abundance of rather coarse mitochondria (fig. 1). These are in 

 the form of coarse granules and curved rods and are distributed quite unfiormly 



