118 



COMPARATIVE PHYSIOLOGY. 



penis, which, becomes a canal. The original opening of the 

 urethra was at the base of the penis. 



In certain cases development of these parts is arrested at 

 various stages, from which result abnormalities frequently re- 

 quiring interference by the surgeon. 



The accounts of the previous chapters do not complete the 

 history of development. Certain of the remaining subjects 

 that are of special interest, from a physiological point of view, 

 will be referred to again ; and in the mean time we shall con- 

 sider rather briefly some of the physiological problems of this 

 subject to which scant reference has as yet been made. Though 

 the physiology of reproduction is introduced here, so that ties 

 of natural connection may not be severed, it may very well be 

 omitted by the student who is dealing with embryology for the 



Fie. 130. — Various forme ol mammalian uteri. A. Omitliorliynclina. B. Didelphye 

 dorBigera. C. Fhalaugista vulpina. D. Double uterus and vagina; liumananoma- 

 I3;. S. Lepus cuniculns (rabbit), uterus duplex. ¥. TJterus bicornis. G. Uterus 

 bipartitus. H. UteruB simplex (human), a, anus; cl, cloaca; 0. £2, oviduct; 0. t, 

 OS tincse (ob uteri); ov, ovary; r, rectum; «, vaginal septum; u. b, nrinary bladder; 

 Mr, ureter; wr. 0, orifice of same; w. s, urogenital sinus; ut^ uterus; v, vagina; v. c, 

 vaginal csecum (Haddon). 



first time, and in any case should be read again after the other 

 functions of the body have been studied. 



THE 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- 



