112 ANIMAL PHYSIOLOGY. 
Fic. 134.—Various forms of mammalian uteri. A. Ornithorhynchus. B. Didelphys dorsigera. 
C. Phalangista vulpina. D. Double uterus and vagina; human anomaly. E. Lepus cuni- 
culus (rabbit), uterus duplex. F. Uterus bicornis. G. Uterus bipartitus. . Uterus 
simplex (human). a, anus; cl, cloaca ; 0. d, oviduct ; 0. t, os tincee (0s uteri); ov, ovary ; 
r, rectum ; s, vaginal septum ; uv. b, urinary bladder ; ur, ureter; wr. o, orifice of same ; 
us, urogenital sinus ; ut, uterus; v, vagina ; v.c, vaginal caecum (Haddon). 
ology for the first time, and in any case should be read again 
after the other functions of the body have been studied. 
Tuer PHYSIOLOGICAL ASPECTS OF DEVELOPMENT. 
According to that law of rhythm which; as we have seen, 
prevails throughout the world of animated nature, there are 
periods of growth and progress, of quietude and arrest of devel- 
opment; and in vertebrates one of the most pronounced epochs 
—in fact, the most marked of all—is that by which the young . 
organism, through a series of rapid stages, attains to sexual 
maturity. ; 
While the growth and development of the generative or- 
gans share to the greatest degree in this progress, other parts of 
.the body and the entire being participate. 
So great is the change that it is common to indicate, in the 
case of the human subject, the developed organism by a new 
name—the “ boy ” becomes the “ man,” the “ girl” the “woman.” 
Relatively this is by far the most rapid and general of all the 
transformations the organism undergoes during its extra-uter- 
ine life. In this the entire body takes part, but very unequally. 
The increase in stature is not proportionate to the increase 
in weight, and the latter is not so great as the change in form. 
The modifications of the organism are localized and yet affect 
the whole being. The outlines become more rounded; the pel- 
