832 The American Naturalist. [October, 
possible to determine what type a given dentition represents. 
In most cases it is clear that, among Colubrid snakes at least, 
no higher groups than genera can be predicated on dentition, 
and frequently not even these. Under such circumstances 
further structural characters had to be sought for if we are to 
have any clear idea of the affinities and phylogeny of this 
curious branch of the Reptilia. In any case no systematic 
arrangement can be regarded as final until the entire anatomy 
is known. 
In 1864' I pointed out that certain snakes, notably the water 
snakes, have the vertebral hypapophyses continued to the tail, 
as in the truly venomous forms. Boulenger has since found 
this character in a good many forms which I had not examined, 
and which have no affinity to the water snakes. This char- 
acter, while important, presents the same evanescent stages in 
certain types that the dental characters before noticed exhibit. 
It had long appeared to me that the only prehensile organs pos- 
sessed by serpents, the hemipenes, might probably present 
structural variations expressive of affinity or diversity. In 
1893’ I examined these structures in many of the leading 
types, and was gratified by the discovery of a great many 
structural characters. In fact these organs exhibit a variety 
of ornamentation and armature beyond any part.of the 
anatomy in the Ophidia, and I am satisfied that they furnish 
more important indication of near affinity than any other part 
of these reptiles yet examined. No one hereafter can be sure 
of the place of a serpent in the system until the hemipenis has 
been examined. 
Still another part of the structure remained to be studied. 
The assymmetry of the lungs of snakes had often been noted 
by anatomists, but very little was known as to the range of 
variation. Accordingly the present year,’ I undertook a study 
of the pulmonary organs. I was able to confirm observations 
previously made by Schlegel and Stannius, and to correct some 
others, and to add a great number of facts as to species not 
! Proceedings Academy of Natural Sciences, Philada. 
 ? American Naturlist, 1893, p. 477. 
-3 Proceeds. Amer. Philos. Soc., 1894, p. 217. 
