472 TRANSACTIONS OF THE CANADIAN INSTITUTE. {Voy. VIIT 
adults while being held lightly by the tail cast off a portion of it, the 
separation occurring in the part grasped and leaving in the one case a 
stump 1 cm. and in the other 1.75 cm. long, measuring from anus to 
end of stump. In no case observed has the length of tail retained been 
less than .5 cm.; it was usually more. There does not seem to be any one 
place where separation greatly tends to occur. Incomplete separation has 
also been noted, the vertebrae and muscles separating but the skin failing 
to break; this causes a slight grooving of the tail as though an invisible 
thread were tied around, compressing it. Longitudinal sectioning was 
used to examine both proximal and distal pieces in those cases that occurred 
under observation, and the relation of parts in the wound was found 
to be as follows, (Figure t.) Separation of the vertebral column occurs 
between vertebrae; this is the condition also in P. oregonensts (Hubbard, 
03). In the muscle the myomeres are not broken but separation occurs 
_in the myocomma opposite the middle of the last vertebra retained. 
The skin however does not break here but at the myocomma opposite 
the middle of the first vertebrae of the piece cast off. Two things are 
accomplished by this; first the wound that now terminates the animal’s 
tail is protected by the extra length of skin which collapses laterally upon 
it and almost covers it in. Second, on the piece cast off considerable 
raw surface is left exposed, the irritation from which is doubtless largely 
responsible for the rapid contortions that occur. This piece must play 
an important part in the protective device for by its violent movements 
it would draw the attention and invite the first attack of an enemy. 
A similar habit has been noted in P. oregonensts by Hubbard (’03) 
but there are distinct points of difference. Briefly in P. oregonensvs 
on moderate stimulation the glands on the dorsum of the tail swell greatly 
and pour out an abundant secretion. Only the most powerful stimu- 
lation—the act of being swallowed by a snake, or being plunged into 
a fixing fluid without previously being anesthetized—would rouse the 
animal to the point of sacrificing its tail. Separation always occurs at a 
constriction just behind the anus. No mention is made of the behaviour 
of the piece separated and, the subject of the paper being correlated 
protective devices, it is perhaps fair to assume that it presents no striking 
peculiarity. In P. cin. eryth. the tail shows neither constriction nor 
swelling nor’ does the great development of dorsal glands occur, the 
thickness of the dorsal skin being one-twelfth to one-eighth of the diam- 
eter of the tail, while it constitutes one-fourth of the swollen tail of P. 
oregonensis. 
Owing to the extreme aversion to light already mentioned it has been 
impossible to ascertain in a terrarium the manner of fertilization of the 
