94 HUMAN BMBKYOLOGY AND MORPHOLOGY. 



by a layer of columnar meso-thelium, the germinal epithelium, 

 which is continuous with the mesothelial lining of the coelom. 

 Some of the columnar cells covering the genital ridge become 

 primordial ova, and are set aside to produce ova or spermatozoa, 

 according to the sex. Beard's researches have led him to the 

 conclusion that primordial ova are produced at a very early stage 

 of development, and that they migrate towards the coelom and take 

 up their position amongst the germinal cells covering the genital 

 ridge when that ridge is formed. These cells may stray and give 

 rise in various parts of the body to dermoid tumours (Beard). The 

 manner in which the germ cells and primordial ova grow within 

 the genital ridge to form the ovary or testicle was described at 

 the beginning of this chapter. The cycle of changes which leads 

 to the production of the ova of one generation from the ovum of 

 a former generation have thus been traced. 



