German.] 
178 
[Jan. 16, 
remotely allied, that bear evidences of effects which are probably 
due to the action of similar causes. 
If we accept the nearly perfect cone on the end of the tail of some 
of the colubrine snakes as the typical button, and compare a num- 
ber of specimens in the same species, we shall find that there is a 
large amount of individual variation. Some caps will be regular, 
others flattened, blunted, or otherwise imperfect in shape. The 
variations are much greater in some species than in others. They 
are especially noticeable in certain genera of venomous serpents be- 
longing to the same family as the rattlesnakes. On the species of 
Bothrops, a South American genus allied to that containing the 
moccasins (Ancistrodon) , there are caps that are compressed, oth- 
ers that are boat-shaped, others awl-shaped, others club-shaped, and 
some that bear slight transverse grooves suggestive of likeness in 
habit to the copperhead. Mhinocerophis ammodytoides of the same 
family illustrates the extreme form of the boat-shaped cap, fig. 9 ; 
and the structure of the interior, fig. 10, indicates that the button 
is applied to and rubbed against the earth. The “mute rattlesnake,” 
Lachesis mutus , a close ally of the large South American rattler, 
Crotalus durissus , has most often the blade-like button shown in fig. 
11 ; its variations include the awl-shaped, and among others the very 
irregular form from which fig. 12 is taken. The latter is a shape 
that must have presented some difficulty in sloughing. From the 
squamation of the tail, and the shape and inclination of the button, 
it is likely this species has a habit of rattling in which the hinder 
portion of the tail is raised from the ground. 
It is not to variations that may affect individuals diversely that 
we must turn for aid in solving the problem of the rattle, but rather 
to a modification that similarly affects all, or at least a considerable 
number of the members of a species. Fortunately, one that is di- 
rectly in line with this study occurs in the North American genus 
Ancistrodon containing the copperhead and the moccasin, and rank- 
ing next to Sistrurus and Crotalus , which include the rattlers. As 
it parallels the development of the cap in the latter to a point little 
short of the attainment of the rattle, we shall devote attention ex- 
clusively to it. 
The moccasin, Ancistrodon piscivorus, is one of the “Water 
Snakes.” It feeds mainly upon fishes, frogs and the like, that fre- 
quent the streams, ponds, marshes and other wet localities. Its 
tail is a little stouter, less flexible, and a little more compressed 
