PHYLOGENY OF VENOMOUS SNAKES 51 



their respective ducti excretores. Among these different Aglyphous species 

 only two seem to lack the rudimentary venom gland or the yellowish portion 

 of the glandula labialis superior. 



One of the most natural outcomes of these morphological investigations 

 would lead to an investigation whether the parotid secretion of these solid- 

 toothed snakes is really toxic when it is introduced directly into the blood 

 circulation of different animals, which are susceptible to the action of the 

 parotic secretion (venom) of some poisonous species. This interesting prob- 

 lem attracted the attention of Bertrand and Phisalix (1894), who discovered 

 that the salivary glands of two European species of Tropidonotus secrete a 

 fluid which acts fatally upon guinea-pigs when injected into them. 



Still later Alcock and Rogers (1902) examined the poisonous property of 

 the watery extract of the parotid of freshly decapitated specimens of Zam- 

 enis mucosus upon rats and mice and of the watery and saline extracts of 

 the parotid and the Harderian glands of Tropidonotus piscator upon the 

 last-named animal. The injection was made subcutaneously. The parotid 

 extract of the Aglyphous snakes used was a viscid mucin, quite different from 

 the thin, opalescent fluid derived from the Opisthoglypha. The violent con- 

 vulsions that followed the injection of Zamenis extract presented a marked 

 contrast to the characteristic dyspnceic convulsions caused by the Opistho- 

 glyphous snakes, although a sufficient dose killed these small mammalia. 

 The extract of the Harderian gland was without toxic effect. 



The poisonous property of the parotid gland, as well as its secretion, of 

 certain harmless, non-groove-toothed snakes, has been established beyond 

 doubt, but there is still much to be done about this problem, especially in 

 regard to the identity of the poisonous principles of these rudimentary forms 

 of the venom glands. A similar investigation of a greater number of non- 

 poisonous snakes and even of the mammalia is highly desirous. 



The passing of snakes from the non-poisonous into the poisonous kinds 

 is a gradual process and is associated with a definite morphological and 

 functional modification of the parts directly concerned. This modification 

 is an acquisition of the poisonous apparatus by grades, namely, the speciali- 

 zation of the supralabial gland into a venomous one, and then the canali- 

 zation of the maxillary teeth so as to enable them to conduct the venom. 

 These changes are also accompanied by an ascending perfection of these 

 and other accessory apparati. Thus, in one group of snakes there is neither 

 the venom gland nor the poison fang. In a second there is the venom gland 

 of a rudimentary stage, but no venom-conducting tooth. In a third the 

 venom gland attains larger dimensions, but the fang is still primitive, being 

 moderate in size, shallow in groove, and situated inconveniently in the rear. 

 In a fourth group the conditions are more favorable, as the venom gland is 

 better developed, the fang is longer and has a deeper groove or a canal, 

 and its position is in the anterior of the maxilla. The fifth and last group 

 has a well-developed gland and one or more large and strong fangs. The 

 fang is tubular and situated in the anterior part of the peculiarly short space 

 of the erectile maxillary bone. 



