EXCRETORY AND REPRODUCTIVE SYSTEMS. 169 



naked eye. In a fresh specimen this protuberance may 

 be picked open and the ovum expelled on a slide for ex- 



J/rm 



FIG. 89. SECTION OF OVARY. X 40. 



sr, Surface of the ovary; gr, Graafian follicle with mature ovum; o, 

 ovum; c, cavity of the follicle; un, undeveloped ova; strm, stroma 

 or connective elements of the ovary; m, membrana granulosa; d, 

 discus proligerus. 



amination with the microscope. The ovum is scarcely 

 visible to the unaided eye. The human ovum is still 

 smaller. 



The ova of all mammals, except the duck-bill and spiny 

 ant-eater, are very small. When the ovum becomes ma- 

 ture, the protruding wall of the follicle bursts, permitting 

 its contents to be received by the expanded end of the 

 Fallopian tube, whence it passes to the uterus. If the male 

 element, the spermatozoon, enters the ovum, the latter is 

 soon enveloped by a growth of mucous membrane and 

 retained in the uterus for development. Ripe ova occur 

 near the close of the first year of the cat's life and new 

 ones probably continue to mature during the next ten years. 

 The discharge of the ova from the ovary is accompanied by 

 a constitutional disturbance, during which an extra amount 

 of blood is sent to the sexual organs, and the sexual appetite 

 becomes very marked. In the human species this dis- 

 turbance occurs about every twenty-eight days. Mature 

 ova occur in the human ovary between the thirteenth and 

 forty-eighth years. 



16 



