64 VIPERID.E. 



having been removed. It is coiled up so closely as almost 

 to appear like a solid mass ; but no sooner is it emancipated 

 than it assumes all the activity and virulence which belong to 

 the species. If a female Viper about to bring forth her young 

 be killed, and the young ones set at liberty by opening the 

 abdomen, they will immediately crawl about, and on being 

 irritated will throw themselves into an attitude of defence. 



A certain degree of temperature, varying in the different 

 classes, is requisite for the developement of the embryo. 

 In the mammalia this temperature is afforded by the standard 

 heat of the body of the parent, within which the young is 

 brought to perfection ; in birds it is also, with few excep- 

 tions, communicated by the parent, but by means of incu- 

 bation, or sitting on the eggs after they are excluded from 

 the body ; in the reptilia, on the contrary, it is communicated 

 solely by the surrounding atmosphere ; and this is equally the 

 case whether the eggs are deposited before the growth of the 

 embryo has commenced, or the young are perfected within 

 the mother, and brought forth alive. In the latter case, as 

 I have already observed, when speaking on the develope- 

 ment of the young of the common Viviparous Lizard, 

 Zootoca vivipara, it is by the exposure of the body of the 

 mother to the sun's rays that the necessary degree of heat is 

 obtained ; and hence during the period of gestation it is very 

 common to see the pregnant female Viper lying, as it were, 

 all abroad, with flattened body, basking in the sunshine ; and 

 at this time she is much less easily disturbed, and more tardy 

 of flight than the male. The number of young produced at 

 each birth varies from twelve to twenty, or even more. 



TheViper, like the other reptilia, seeks a secret and secure 

 place in which to hibernate during the cold months of the year. 

 Here several are found entwined together, and in a very tor- 

 pid condition; and if at this period a Viper be made to wound 

 an animal with its poison-fang, no injury is likely to result 



