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- 
Fic. 89. SEcTIoN oF Ovary. X 40. 
sr, Surface of the ovary; gr, Graafian follicle with mature ovum; 0, 
ovum; c, cavity of the follicle; uw, 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 
