124 PLANTS WITH TRAPS AND PITFALLS TO ENSNARE ANIMALS. 
In each pitfall there are always three kinds of contrivance to be distinguished: 
first, a device for the allurement of animals; secondly, an arrangement for entrap- 
ping the prey enticed, which at the same time prevents individuals once imprisoned 
from returning and escaping through the entrance hole; and thirdly, a structure 
for causing the decay or dissolution of the dead animals at the bottom of the pit- 
falls, and for rendering possible the absorption of the products of decomposition 
as nutriment. The means of allurement are similar to those which cause the visits 
of small creatures to flowers, that is to say, principally honey and bright and 
varied coloration, whereby the nectar-secreting spots are recognized from afar, 
especially by flying insects. The escape of animals when they have once entered 
the cavity of a petiole is prevented, as has been already mentioned, by a fringe 
of sharp hairs pointed downwards, or by various spinous structures on the inner 
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Fig. 19.—Spinous Structures in the Pitfalls of Carnivorous Plants. 
1 Genlisea; a piece of the tube seen from inside. 2 Heliamphora nutans; spines on the walls of pitfalls. % Sarracenia 
purpurea; a piece of the lining of the pitcher near the orifice seen from inside. 4 Sarracenia purpurea; longitudinal 
section through the membrane covered with spinous bristles in the lower part of the pitcher. 5 Nepenthes hybrida; 
fringe of spines at the orifice of the pitcher. 1, 2, 4, 5 greatly magnified; 3 slightly magnified. 
surface of the cavity. The decomposition and dissolution of the prey are effected 
by fluids secreted by special cells at the bottom of the utricles and pitchers. 
But although in respect of the consecutive and co-ordinate operation of these 
three kinds of contrivance, all ascidia-bearing and pitcher-plants resemble one 
another, there are considerable individual divergences as to structure and function 
that it is well worth while to study in some detail the most noticeable of them. 
One of the most noteworthy is the genus @enlisea, which is nearly related to 
Utriculariacez in the structure of its flowers and fruit. It is composed of a dozen 
species growing in water and marshy places. Of these one is a native of tropical 
and southern Africa, whilst others are found in Brazil and the West Indies. In 
addition to ordinary leaves, which in them are spatulate, most of the Genlisexe 
possess leaf-structures metamorphosed so as to constitute pitfalls. Each pitfall 
consists of a long, narrow, cylindrical utricle, which at its blind end is enlarged 
into a bladder, whilst at the narrow orifice at the opposite end are placed two 
peculiar ribbon-shaped processes twisted spirally. The orifice of the utricle is set with 
very small sharp teeth bent inwards; and the tubular part of the utricle has its 
inner surface lined throughout with innumerable little bristles, which arise from rows 
