536 



B O A. 



that one full meal serves for weeks ; and, for a con- 

 siderable time after it is taken, the whole energy of 

 the animal appears to be so completely absorbed by 

 the work of digestion, and its powers both of attention 

 and of motion so completely deadened, that it makes 

 no attempt at resistance or even at escape. When 

 hungry or otherwise excited, these animals are very 

 formidable, and their motions are so quick, and their 

 strength in crushing is so great, that it is very hazard- 

 ous to approach them ; but when they have taken a 

 full meal, a naked savage may with impunity go in 

 upon the most powerful of them, and fell it by blows 

 on the head with a club; and so completely are its 

 faculties engrossed by the inward labour of digestion, 

 that instead of making efforts to escape from the 

 blows, it hardly writhes under them, but dies with the 

 same comparative quiet as it is then bearing. 



There is some confusion between this and some of 

 the nearly allied genera, as there is about most of the 

 serpents, and indeed of the whole class of reptiles 

 generally speaking, so that the character and conduct 

 of one have sometimes been ascribed to another. 

 There is a nroneness to exaggerate every thing about 

 reptiles, and there is a popular aversion, which those 

 who have the best opportunities of examining them 

 have not always the power of overcoming. Besides, 

 their habits are obscure and retiring ; and in order to 

 be observed, they must be searched out with more 

 diligence than most animals. The places which they 

 frequent are also not the most inviting, or even the 

 most safe ; they are the tangled brakes and margins 

 of marshes in very hot climates, which are unhealthy, 

 and though the reptile of which the observer is in 

 search may not be venomous itself, there is no 

 knowing where venomous ones may be lurking ; and 

 as these are usually smaller and more easily put in 

 motion than the larger ones which are not venomous, 

 it requires no small nerve as well as caution to thread 

 the serpents' preserve with the requisite degree of 

 attention. Hence, there are probably more unde- 

 scribed or inaccurately named and described speci- 

 mens of reptiles in the collections and museums, than 

 there are of all the other vertebrated animals taken 

 together. 



The form and number of the scales, especially 

 those on the under side of the body and tail, have 

 been, in the true serpents, among the chief means of 

 generic distinction. These scales are their proper 

 organs of locomotion, and the only external organs, 

 excepting such as appear on the head or are attached 

 to the extremity of the tail. The external means of 

 distinguishing one serpent from another, when they 

 are in their proper haunts in free nature, are therefore 

 not only much more limited than in the case of ani- 

 mals which have feet or wings, or even fins. They 

 are also obscure, because the parts are small and in- 

 conspicuous, and if the number or the form of. the 

 scales are the only distinguishing characters, then the 

 species or even the genus of a serpent cannot be 

 ascertained, unless it is killed or captured. 



This uncertainty is the cause of another : for, as we 

 cannot understand the character of the one which 

 gets away, we are not sure whether those foundations 

 of character which we adopt are constant or not. 

 We know that, in some of the species, the number of 

 cartilaginous pieces which form the rattle at the extre- 

 mity of the tail, increases with the age of the animal, 

 and also that some of them are apt to be broken off 

 by accident; and it may be possible that the number 



and also the form of the scales on others change with 

 age. Colour too is, though necessarily relied on in 

 cases where the means of distinction are so few, not 

 worthy of implicit confidence, especially when we 

 come to the nicer distinction of individuals which 

 have a very strong general resemblance to each other. 

 These difficulties, and taking them altogether they 

 are of a kind not easy to be removed, are but too 

 good an apology for the mist of obscurity which 

 hangs over this department of natural history, and 

 renders it so dark that he who writes on it with the 

 greatest apparent confidence is generally the least 

 worthy of credit. 



Taking the distinctive character from th,e scales on 

 the under part of the belly and tail, the tribe or 

 family of boa comprehends all those serpents which 

 have these scales entire, or of one plate extending 

 from side to side without any joint upon the mesial 

 line, and which at the same time have neither a 

 rattle nor a spinous prolongation at the end of the tail. 

 It is by this series of single scales that the family boa 

 is distinguished from coluber, in which there are two 

 rows of scales along the same part ; but there have 

 been specimens observed with some of the scales on 

 the under part double, while the majority were single. 

 It should seem that the larger crushing serpents of 

 the south-east of Asia belong to the coluber family, 

 and to the genus or sub-genus python (see COLUBER), 

 while the larger species of true boa are found only in 

 the tropical parts of America; and they seem to be 

 found nearer the water, and generally to inhabit more 

 humid places than the pythons of the East. 



The boas have a spinous hook at each side of the 

 vent, the body compressed, and the tail prehensile, 

 or capable of holding on by a tree or a branch, while 

 the rest of the body coils round the captured animal, 

 and sometimes draws it toward the tree, where it is 

 crushed to death. The scales upon the upper part 

 of the body and hinder part, of the head are small. 

 The structure of the head and jaws varies considerably, 

 and gives rise to some subdivisions of the genus. 



Some of the species attain a very large size, mea- 

 suring thirty or forty feet in length ; and when they 

 are of that size they can master deer and even buffa- 

 loes. Their mode of killing is always by crushing in 

 the coils or folds of their bodies, rf the prey is so 

 large as to require that operation ; and they lick or 

 smear it all over with their glutinous saliva, before 

 they begin to swallow it. When the prey is of 

 smaller size, they seize it at once in the vast opening 

 of their mouths. 



No one who sees those animals only in a state of 

 inaction, and with the mouth shut, and the neck of 

 of the usual dimensions which it has in that state, 

 would readily form an idea of the vast extent of their 

 gape and the wideness of their gullet; but the one 

 and the other will so open as to take in an animal of 

 much greater diameter than the serpent itself. All 

 the true serpents have the under jaw articulated in a 

 peculiar manner, which will be explained in the article 

 OPHIDJA ; but we may mention here that the lower 

 jaw is not articulated upon the bones of the cranium, 

 but upon two additional bones; and that these again 

 are not articulated upon the bones of the cranium, 

 but attached by muscles and ligaments, which admit 

 of considerable extension. A portion of the anterior 

 part of each jaw is also formed of ligaments or tendi- 

 nous matter, which is flexible and capable of being 

 stretched. 



