132 
JOURNAL OF MAMMALOGY 
the lengths of breath, i.e., the time that the nostrils are open, is about 
the same for the young, 30— seconds, that it is for the male, 27 -f 
seconds, and for the female, 30— seconds. In other words, the actual 
breathing operation occupies an interval of time which was about 
the same for all three manatees. This unit is used in small multiples 
by the young, 1.7— in larger multiples by the male, 2.2, and in still 
larger ones by the female, 2.6. 
The interval between two breathing periods is the resting period 
during which the manatee is reposing quietly under water. During 
this interval the animal is cut off from its supply of air and hence the 
length of this period is a measure of its adaptation to submergence. 
The resting period in the young varied from 2 minutes to 9 minutes 
and 30 seconds with an average of 4 minutes and 37— seconds; in the 
male it ranged from 4 minutes and 40 seconds to 13 minutes with an 
TABLE 2 
Average breathing 'periods in minutes and seconds, average numbers of breaths in 
each breathing period, average resting period in minutes and seconds, and average 
length of breath in seconds for the three manatees recorded in table 1. The results 
are computed from the figures in that table 
YOUNG 
MALE. 
FEMALE. 
Breathing periods 
:49 
1:00 
1:174- 
Number of breaths 
1.7— 
2.2 
2.6 
Resting periods 
4:37— 
8:38- 
12:01- 
Lengths of breath 
:S0— 
:27+ 
:30- 
average of 8 minutes and 38— seconds, and in the female it varied 
from 7 minutes and 20 seconds to 15 minutes and 10 seconds with an 
average of 12 minutes and 1 — second. In general it may be said that 
taking the period of submergence in the young as unity that in the 
male was nearly two and that in the female nearly three. 
As the young manatee was the smallest of the three, the male next 
in size, and the female the largest, there appears to be a fairly intimate 
relation between the size of the animal and its respiratory activities, 
for the larger the manatee the longer its breathing period, the greater 
its number of breaths in each such period and the longer it remained 
under water. 
A number of other sets of records were taken from the manatees in 
addition to those given in table 1, but these sets were incomplete as 
compared with the three already tabulated in that, instead of extending 
