THE ADDER. 153 



mate, but founded on the specific data stated, and it 

 is that the average number of young of the adder is 

 about IS. 



Development. — The terms viviparous and ovo-vivip- 

 arous are both used to describe the method of birth 

 in adders. Both are correct : viviparous — in that it 

 means that the young are brought forth alive ; ovo- 

 viviparous — in that the term means that the young 

 are extruded cdive 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 descrip- 

 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 briefly 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 eggs the following 

 size and shape. 



Fig. 34. — Eggs of Adder. 



On section, to the naked eye they appeared to be 

 full of yolk. A month later, on June 14, a speci- 



