140 



KNOWLEDGE. 



[June 1, 1894. 



specialization seems, indeed, to have taken place in certain 

 members of the group, which have adopted a mode of life 

 in which these organs would be useless. An excellent 

 instance of this is afforded by the venomous sea-snakes of 

 the warmer oceans, the typical members of which are 

 purely pelagic in their habits, and have the under surface 

 of the body covered either with small scales, or retaining 

 mere vestiges of the large shields. That this departure 

 from the ordinary type is a specialized character is, 

 fortunately, demonstrated by one genus of these serpents 

 (Platiirus), the members of which are partly terrestrial 

 in their habits, and consequently retain the large inferior 

 shields. All the burrowing blind snakes, so widely dis- 

 tributed over the warmer regions of the globe, together 

 with members of several groups which have taken to 

 purely arboreal Ufe, have likewise lost the large inferior 

 shields, as bemg no longer useful. 



In the pre-Darwinian days of natural history it was 

 doubtless considered that snakes were created as such, 

 and that they were always "rib-walkers." The modem 

 naturalist, however, knows better than this, since some of 

 the members of the group, fortunately, retain vestiges 

 which enable him to say with confidence that serpents are 

 the highly modified descendants of four-legged reptiles, 

 more or less nearly akin to lizards. Among the better- 

 known members of the group, pythons and boa-constrictors, 

 collectively constituting the family Boiidce, are those 

 alone retaining such vestiges, which externally take the 

 form of a pair of claw-like spurs situated on the lower 

 surface near the junction of the body with the tail. If, 

 moreover, we dissect such a snake, it will be found that 

 traces of the three bones of the pelvis are imbedded among 

 the muscles, although now of no functional importance 

 whatever. And if such rudiments are not to be regarded 

 as indicative of the descent of snakes from reptiles furnished 

 with hmbs, we may as well give up trying to apply philo- 

 sophical reasoning in zoology. 



Putting aside the little-known group of blind snakes, 

 the pythons and boas are indeed the most primitive of all 

 serpents, and the more typical members of the group are 

 distinguished by their habit of destroying their prey by 

 " constriction." All pythons and boas, it is perhaps well 

 to observe, are non-venomous, and the family includes by 

 far the largest representatives of the entire ophidian group. 

 The excellent photographs with which this article is 

 illustrated were taken by Mr. Eanyard inside the cage of 

 the python, at the Zoological Gardens, Eegent s Park. 

 Formerly it was attempted to arrange all the other and 

 more specialized snakes, in which traces of the hind limbs 

 have completely vanished, into families, according as to 

 whether they were innocuous or venomous ; but modern 

 research has shown that such divisions are piu-ely arti- 

 ficial, and that the development of poison-bearing organs 

 has originated independently in several distinct groups, 

 thus affording another excellent example of parallelism. 

 There is, however, one family of snakes ( r;>«n'rf«), including 

 the ordinary vipers and rattle-snakes, all the members 

 of which are venomous, and may be distinguished from 

 the members of the other great family by the circumstance 

 that when the jaws are opened the maxillary bones, in 

 which are implanted the pair of long tubular poison- 

 fangs, become erected at right angles to the hinder part, 

 thus giving to the teeth the most powerful mode of 

 action possible. The other great family of limbless 

 snakes {Cohihrida) comprises both harmless and poisonous 

 forms, and is distinguished from the viper family by the 

 absence of the power of erecting the maxillary bones. 

 These snakes, which include by far the greater majority 

 of the entire group, are remarkable not only for the extra- 



ordinary adaptability to different modes of life they display 

 — some of them being terrestrial, others arboreal, others 

 fluviatile, and others marine — but still more for the cir- 

 cumstance that members belonging to totally different 

 sections of the family have become independently modified 

 to similar modes of life, and have thus acquired an external 

 similarity which effectually masks their structural differ- 

 ences. Their true relationships appear to be best revealed 

 by the structure and arrangement of the teeth ; and on this 

 e\-idence they are divided into three parallel sections, each 

 of which shows a very similar series of adaptations to 

 particular modes of life. In the first great section, or 



Side view of the Head of the Pythou at the Zoological Gardens. 

 The fold beneath the head and neck is more than six inches thick. 



solid-toothed colubrines, the whole of the teeth are solid 

 and frequently subequal in size ; and it is, therefore, 

 evident that all the members of the group (in which is 

 included the common English ringed-snake), are perfectly 

 harmless. In a second section, which may be termed the 

 hind-fanged colubrines, one or more of the hinder upper 

 teeth are enlarged and grooved ; and it would appear that 

 the majority of the group are more or less poisonous. 

 Among these snakes are the well-known arboreal whip- 

 snakes {Dri/ojihis) and sand-snakes {Pnaiinn(ip/iis). The 

 front-fanged colubrines, which are far more deadly, differ 

 from the last in having the front teeth in the maxillary 

 bones enlarged and either grooved or tubular for the 

 purpose of carrying the venom from the poison-gland to 

 the woimd. This section includes the dreaded Indian 

 crait, as well as the cobras of Asia and Africa, both of 

 which are to the full as deadly as any of the vipers ; while 

 the sea-snakes also belong to it. That the front-fanged 

 and hind-fanged colubrines have acquired their venomous 

 properties entirely independent of one another is perfectly 

 evident from the different position of the teeth modified for 

 this purpose ; and the wide structural difference between 

 the vipers and colubrines shows that the former have no 

 sort of connection with either of the sections of the latter. 

 We have, accordingly, clear evidence of the development 

 of poison-glands and fangs in three totally independent 



