324 ALDROVANDA VESICULOSA. Cnap. XIV. 
prominence. These processes are formed of very 
delicate membrane lined with a layer of protoplasm ; 
and they sometimes contain aggregated globules of 
hyaline matter. Two of the slightly diverging arms 
are directed towards the circumference, and two 
towards the midrib, forming together a sort of Greek 
cross. Occasionally two of the arms are replaced by 
one, and then the projection is trifid. We shall see in 
a future chapter that these projections curiously re- 
semble those found within the bladders of Utricularia, 
more especially of Utricularia montana, although this 
genus is not related to Aldrovanda. 
A narrow rim of the broad flat exterior part of each 
lobe is turned inwards, so that, when the lobes are 
closed, the exterior surfaces of the in-folded portions 
come into contact. The edge itself bears a row of 
conical, flattened, transparent points with broad bases, 
like the prickles on the stem of a bramble or Rubus. 
As the rim is infolded, these points are directed 
towards the midrib, and they appear at first as if they 
were adapted to prevent the escape of prey ; but this 
can hardly be their chief function, for they are com- 
posed of very delicate and highly flexible membrane, 
which can be easily bent or quite doubled back with- 
out being cracked. Nevertheless, the infolded rims, 
together with the points, must somewhat interfere 
with the retrograde movement of any small creature, 
as soon as the lobes begin to close. The circum- 
ferential part of the leaf of Aldrovanda thus differs 
greatly from that of Dionza; nor can the points on 
the rim be considered as homologous with the spikes 
round the leaves of Dionza, as these latter are pro- 
longations of the blade, and not mere epidermiec 
productions. They appear also to serve for a widely 
different purpose. 
