THE EGG 



glandular body occupying the site of the follicle (Plate IX, 

 Ai B). As the lining grows thicker, blood vessels creep in from 

 the surrounding part of the ovary and make a network that 

 carries blood past every one of the large cells (Plate IX, C). 

 These cells become laden with a peculiar kind of fatty mate- 

 rial, and in animals whose fat is yellowish, for example the 

 cow, the transformed follicles are bright yellow in hue, becom- 

 ing indeed just about the most brilliantly colored objects in 

 the whole body. For this reason they were long ago named 

 corpora lutea, yellow bodies ; but in animals whose body fat 

 is white, as the sow, sheep, rat, and rabbit, they appear pink 

 or whitish. The human corpus luteum forms a mass almost 

 three-quarters of an inch in diameter, with a folded wall, 

 bright orange in color, about a grayish core of fibrous tissue. 



Animals which shed one egg at a time have, of course, only 

 one corpus luteum in each cycle of the ovary ; animals which 

 bear multiple litters have a corpus luteum for each egg, i.e. 

 for each follicle that ruptured. The sow averages ten corpora 

 lutea in a batch, and may have twenty-five, which is the num- 

 ber of the largest litter of pigs ever recorded. The rat can 

 have eighteen, the guinea pig two to four, dogs of various 

 breeds as many corpora lutea as there are puppies in the 

 litter of the breed.* 



These yellow bodies of the ovary have been puzzling to 

 scientists ever since they were first described by Regner de 



3 There are interesting exceptions to the statements in the foregoing 

 paragraph. In the first place, human females occasionally shed two eggs 

 at one time; if both are fertilized twins will be produced. In the case 

 of identical twins there is only one egg, which forms two infants. 

 Triplets usually come from two eggs, one of which gives twins. In the 

 case of the Dionne quintuplets it is conjectured from indirect evidence 

 (i.e. the close resemblance of the 5 sisters) that they all came from one 

 egg. In animals with multiple litters it is often the case that not all the 

 fertilized eggs develop successfully; then obviously there will be more 

 corpora lutea in the ovary than infants in the litter. On the other hand 

 it is possible, though uncommon, to have more infants than corpora 

 lutea, for one follicle may contain two eggs (a rare event) or one or more 

 of the eggs may develop into single-ovum twins. 



{ i3 } 



