The Intra-Uterine Growth-Cycles of the Guinea-Pig. 713 



in the fifth column) represents the weight of placentae, amniotic fluid 

 and blood lost at birth, as well as the growth of the mother. The 

 mother's growth can be obtained separately by getting the difference 

 between the weight at copulation and just after delivery. A figure 

 thus obtained however, would represent two kinds of growth, namely, 

 1) continuous growth of the mother, and 2) fat accumulated during preg- 

 nancy. This accumulation of fat during the period of gestation 

 seems to be a general phenomenon and is especially to be noted in 

 the case of the guinea-pig, the milk of which contains such a high 

 percentage of fat 1 ). For our purpose, we will disregard as far as 

 we can, everything which is not growth of young in utero; this is 

 represented by the value in the fifth column of Table II. 



Table III is an illustrative page of the calculations showing the 

 figures for A 2 , Bp 2 , and K t . The weight of the mother on every 

 second day is placed in the first column and in the second appears 

 the increase at each period over the weight at copulation. The last 

 value in the second column corresponds to that in the third column 

 of Table II. 



Since we are concerned here with the increase in the weight 

 of the litter only, it becomes necessary to eliminate the growth due 

 to placentae and fat accumulated by the mother, in short, everything 

 not representing the growth of the litter. We have only one deter- 

 mination upon the weight of the litter itself, that is, its weight just 

 after birth. The difference between the weight of the litter and 

 the total increase in the mother's weight during gestation is the value 

 representing all increase in weight other than that of the litter. But 

 this extra weight has accumulated along with the young in utero, 

 so in eliminating it we must distribute it over the whole period of 

 gestation. In order to eliminate this weight justly and to distribute 

 it proportionally throughout the whole period, the following method 

 has been adopted. A horizontal line was ruled off on coordinate 

 paper. It represented by its length the number of days of gestation, 

 each day being represented by one space on the paper. At the 

 right end of this line a perpendicular was erected which correspon- 

 ded in height to the value in the fifth column of Table II. Each 

 space represented one gram. A right-angled triangle was formed 

 when the free ends of the horizontal and perpendicular lines were 

 joined by a straight line, which formed the hypotenuse. The distance 



*) J. MARION BEAD, Observations on the suckling period in the guinea- 

 pig. University of Cal. publications in Zoology. Vol. 9. pp. 342, 343. 



