Chapter XIV 



— 253 — 



The Utricularia Trap 



to touch on the tripping bristles. In still another case, a very slender 

 bit of a swallowed shred remained protruding, and the walls of the 

 trap had become concave. The delicacy of this protruding shred had 

 permitted the door to take the set posture, allowing full exhaustion of 

 the internal water. On stimulating the tripping hairs, this shred was 

 swallowed. 



It is evident from these experiments that: i. When the prey is 

 soft and yielding, but, caught part way in, is large enough to prevent 

 the door from taking the set posture, this still may clamp down 

 enough to enable the trap walls to bring about a sufficiently low 

 pressure to exert suction and thus draw in the body of the prey and, by 

 repetition, finally engulf it, if small enough. 



E F G H 



YiG. 8. — The sucking in of prey by the trap of Utriciduria gibba or a related species; 

 A, an injured mosquito larva was presented and suddenly but only partly swallowed, 

 May 21, 1941; B, the same three days later; C, a shred of albumen presented and partly 

 swallowed at 11:20; D, at 11:38, the shred entirely swallowed (the insert figure indicates 

 the edge of the door looped over the soft and yielding prey, the surface of the threshold 

 indicated by the broken line); E, a shred of albumen presented at 11:35, and the trap 

 observed continually; F, at 11:37, part of the shred indicated by a double arrow had been 

 slowly sucked in; G, at 11:43, the door quickly (but not very suddenly) opened and 

 another portion of the shred (/) swallowed; later (H) the remainder was engulfed. 



2. If the prey is slender and yielding enough, the door may assume 

 a sufficiently exact set posture to insure the full setting of the trap, 

 when it will react normally but, of course, only in response to move- 

 ment of the tripping bristles. When the prey, still not engulfed, 

 dies, it may not be swallowed unless the tripping bristles are touched 

 by some other agent. If a stiff, unyielding object such as a hair is 

 used (as did Czaja), this cannot happen because of inleakage of water 

 at the side of the hair. 



Traps which have captured mosquito larvae (the head remaining 

 protruding) do not survive, dying in 10 days or so, evidently from 

 overfeeding. 



We now resume our discussion of the structure of the trap. In 

 addition to the front view of the velum, which can be seen in the living 

 trap, a side view can be had under favorable conditions, when it is 

 seen that the velum forms a bolster in front of the door edge (25 — 3,4). 



