xl 
INTRODUCTION. 
though, in order to obtain a greater intensity of eolour, I 
allowed a drop of violet-juice to dry on each plate of the 
compressorium , so that with a power of 800 diameters, the 
whole field was of a deep uniform translucent blue — still 
the ejected wire produced no change of tint. 
Such a test as this is not sufficient to prove that no acid 
or alkaline property exists in the discharged fluid, and still 
less that no poisonous fluid at all is effused ; since that 
most concentrated poison, the venom of the rattlesnake, is 
said to change vegetable blues to reds, in so slight a degree 
as to be scarcely perceptible* 
Admitting the existence of a venomous fluid, it is diffi- 
cult to imagine where it is lodged, and how it is injected. 
The first thought that occurs to one’s mind is, that it is the 
organic fluid which we have seen to fill the interior of the 
cnida, and to be forced through the everting tubular eciho- 
rceum. But if so, it cannot be ejected through the ex- 
tremity of the ectTio7'oeum, because if this were an open 
tube, I do not see how the contraction of the fluid in the 
cnida could force it to evolve; the fluid would escape 
through the still inverted tube. It is just possible that 
the barbs may be tubes open at the tips, and that the 
poison-fluid may be ejected through these. But I rather 
incline to the hypothesis, that the cavity of the ectliorcBum 
in its primal inverted condition while it yet remains coiled up 
in the cnida, is occupied with the potent fluid in question, 
and that it is poured out gradually within the tissues of 
the victim, as the evolving tip of the wire penetrates farther 
and farther into the wound. 
I 
Perhaps it is not too much to say that the whole range of 
organic existence does not afford a more wonderful example 
than this, of the minute workmanship and elaboration of 
the parts, the extraordinary mode in which certain pre- 
scribed ends are attained, and the perfect adaptation of the 
contrivance to the work which it has to do. 
* In a communication made by Dr. M'Donnell to the Royal Society, 
some experiments were detailed, which bad led the observer to believe that 
electricity was the power in question. In a subsequent paper, however, 
that gentleman gave up his hypothesis. {Proc. Roy. Soc. Jan. 14, and 
Nor. 18, 1858.) 
