THE ADDER. 153 
mate, but founded on the specific data stated, and it 
is that the average nwmber of young of the adder is 
about 13. 
Development.—The terms viviparous and ove-vivip- 
arous are both used to deseribe the method of birth 
in adders. Both are correct: viviparows—in that it 
means that the young are brought forth alive ; ovo- 
viviperous—in that the term means that the young 
are extruded alive from an egg-covering. The latter 
term is therefore more descriptive than the former, as 
it includes an additional fact. 
It would be out of place in a work of this deserip- 
tion to discuss microscopic appearances ; but it is of 
interest to the field naturalist to observe the size and 
shape of the eggs and the embryos at different stages, 
and these may be brietly noticed. 
Before the embryos can be distinguished in the 
egg, say in May, the eggs are long and somewhat 
the shape of a very short thick cigar. A specimen 
taken on May 16 showed the eges the following 
size and shape. 
LITTON 
JF —_ 
“Wale ests 
Eaas or ADDER. 
Kia. 34, 
On section, to the naked eye they appeared to be 
full of yolk. A month later, on June 14, a speci- 
