108 DISTRIBUTION OF MITOCHONDRIA IN THE PLACENTA. 



through the protoplasm. Just beneath the basement membrane is a rich capillary 

 network which rests on the connective-tissue stroma containing the maternal blood- 

 vessels and uterine glands. The mitochondria of the connective-tissue cells and of 

 the endothelium are similar to those of the corresponding cells in the chorion. 



The uterine glands are lined by a single layer of medium-sized columnar epithe- 

 lial cells 15 to 20 IJL in height. Each cell contains a single round nucleus, located 

 near the base of the cell, which stains light green and has a well-defined chromatin 

 network and one to four fuchsinophilic nucleoli. The cell protoplasm stains a 

 faint green and contains a rather large number of mitochondria, most of which are 

 in the form of heavy, slightly curved rods (fig. 2). A few medium-sized granular 

 mitochondria are found in either extremity of the cell. The rods are all arranged in 

 the long axis of the cell and often a single rod extends the entire distance from the 

 base to the apex of the cell. Many of these cells contain coarse globules of a substance 

 similar in staining to the mitochondria. These are larger in diameter than the 

 mitochondria and fairly uniform in size. In senile cells with pycnotic nuclei they 

 may entirely replace the mitochondria. They are not uncommon, however, in the 

 apical zones of apparently normal cells. In cells in a later stage of degeneration 

 the globules are replaced by vacuoles. 



The muscle fibers of the pregnant uterus contain numerous minute mitochon- 

 dria in the form of short rods and granules. They are very numerous in a narrow 

 zone around the nucleus and fairly numerous in the peripheral zone of the muscle 

 fiber just beneath the fiber sheath. In lesser numbers they are scattered through 

 the substance of the fibers. 



PLACENTA OF THE CAT. 



In the cat the placental labyrinth consists of alternating columns of fetal 

 ectoderm and loose connective tissue. The maternal blood-vessels occupy the 

 center of the ectodermal columns, while the fetal vessels are located in the connective 

 tissue separating them. The layer of ectoderm surrounding the maternal blood- 

 vessels is composed of giant cells and numerous smaller cells. The cytoplasm of the 

 latter coalesces gradually, as gestation advances, to form a syncytium which 

 incloses the maternal blood-vessels and the giant cells. 



The cells lining the maternal vessels differ from ordinary endothelium in that 

 their protoplasm is slightly more abundant and much richer in mitochondria 

 (fig. 3). The mitochondria are so numerous that, unless the preparation is very 

 thoroughly differentiated, the protoplasm of these cells stains a uniform deep red. 

 In a well-differentiated section, forms varying from fine to coarse granules and curved 

 rods are seen closely packed in the faint green protoplasm. The nuclei stain light 

 green and have a green-staining nucleolus as in ordinary endothelium. In the 

 earlier stages of the placenta these cells possess more abundant protoplasm rich in 

 small mitochondria. 



The giant cells, isolated or in small groups, alternate with the maternal vessels 

 to form the center of the column. Occasionally, giant cells lie alongside of a maternal 

 vessel between it and the border layer of tetal ectoderm. These are round to oval 



