GENERATION AND DEVELOPMENT. 243 



indications of the commencement of puberty in the female sex; though 

 its absence even for several years is not necessarily attended with arrest of 

 the other characters of this period of life, or with inaptness for sexual 

 union, or incapability of impregnation. The average time of its first ap- 

 pearance in females of this country and others of about the same latitude, 

 is from fourteen to fifteen; but it is much influenced by the kind of life 

 to which girls are subjected, being accelerated by habits of luxury and 

 indolence, and retarded by contrary conditions. On the whole, its ap- 

 pearance is earlier in persons dwelling in warm climes than in those in- 

 habiting colder latitudes; though the extensive investigations of Eobertson 

 show that the influence of temperature on the development of puberty 

 has been exaggerated. Much of the influence attributed to climate 

 appears due to the custom prevalent in many hot countries, as in Hin- 

 dostan, of giving girls in marriage at a very early age, and inducing sex- 

 ual excitement previous to the proper menstrual time. The menstrual 

 functions continue through the whole fruitful period of a woman's life, 

 and usually cease between the forty-fifth and fiftieth years. 



The several menstrual periods usually occur at intervals of a lunar 

 month, the duration of each being from three to six days. In some 

 women the intervals are as short as three weeks or even less; while in 

 others they are longer than a month. The periodical return is usually 

 attended by pain in the loins, a sense of fatigue in the lower limbs, and 

 other symptoms, which are different in different individuals. Men- 

 struation does not usually occur in pregnant women, or in those who are 

 suckling; but instances of its occurrence in both these conditions are by 

 no means rare. 



CORPUS LUTEUM. 



Immediately before, as well as subsequent to, the rupture of a Graafian 

 vesicle, and the escape of its ovum, certain changes ensue in the interior 

 of the vesicle, which result in the production of a yellowish mass, termed 

 a Corpus luteum. 



When fully formed the corpus luteum of mammiferous animals is a 

 roundish solid body, of a yellowish or orange color, and composed of a 

 number of lobules, which surround, sometimes a small cavity, but more 

 frequently a small stelliform mass of white substance, from which delicate 

 processes pass as septa between the several lobules. Very often, in the 

 cow and sheep, there is no white substance in the centre of the corpus 

 luteum; and the lobules projecting from the opposite walls of the Graafian 

 vesicle appear in a section to be separated by the thinnest possible lamina 

 of semi-transparent tissue. 



When a Graafian vesicle is about to burst and expel the ovum, it be- 

 comes highly vascular and opaque; and, immediately before the rupture 



