334 THE ZOOLOGIST. 



famine, might primarily cause a preponderance of male births, 

 and subsequently, if at all recurrent, bring about a diminution 

 of individuals ; in other words, unusual meteorological condi- 

 tions might seriously diminish that portion of a flora absolutely 

 important to the nutriment of a dependent fauna, and so, with- 

 out actually causing starvation, might effect a preponderance 

 in male births, and also the introduction of a weakening or 

 destructive element advancing the decline which precedes the 

 fall. 



This brings us to the consideration of droughts and their 

 primary and secondary consequences. It is extremely difficult 

 to focus the information on this subject, as it is scattered about 

 in different publications of various nationalities. Even when 

 found often little is recorded, and where fuller records exist 

 they are often inaccessible. Darwin of course has observed 

 and graphically recorded the effect of drought, when travelling 

 in South America. " The period included between the years 

 1827 and 1830 is called the ' gran seco,' or the great drought. 

 During this time so little rain fell that the vegetation, even to 

 the thistles, failed ; the brooks were dried up, and the whole 

 country assumed the appearance of a dusty high road. This 

 was especially the case in the northern part of the province of 

 Buenos Ayres and the southern part of St. Fe. Very great 

 numbers of birds, wild animals, cattle, and horses perished from 

 the want of food and water. . . . The lowest estimate of the 

 loss of cattle in the province of Buenos Ayres alone was taken at 

 one million head. A proprietor of San Pedro had previously to 

 these years 20,000 cattle ; at the end not one remained." * We 

 can well imagine the effect that an occasional drought like this 

 must cause to much animal and vegetal life, but, when droughts 

 are recurrent, extinction rather than depopulation must ensue to 

 many species in the course of time. Darwin himself further 

 remarks : " These droughts to a certain degree seem to be almost 

 periodical ; I was told the date of several others, and the intervals 

 were about fifteen years." t Livingstone has described a similar 

 infliction in South Africa : " The place where we first settled 

 with the Bakwains is called Chonuane, and it happened to be 



* ' Journ. Eesearch. Voy. Beagle,' pp. 132-133 (1860). 

 •f- Loc. cit. p. 134, note. 



