THE BLADDERS IN UTRICULARIA VULGARIS. 405 
This region presents a slight concavity when viewed from outside. From 
this coneavity, mainly at the sides, arise numerous club-shaped glandular 
hairs (fig. 3, a). These are each composed of three cells: (1) an attaching 
stalk cell, more or less elongated : (2) a short (square in section) middie 
cell; and (3) a swollen distal cell forming the club. Similar hairs to this 
occur round the rim, but they are most common dorsally. The middle region 
of the valve bulges slightly outwards from the bladder normally. The cells 
of the outer layer of this region are similar to the special cells of the next 
region in that their walls have some ridges projecting internally, mainly at 
the angles of the cells. The inner layer is composed of larger, thin-walled 
cells, which from their structure would readily allow an inward flexion of the 
valve (fig. 5). 
Marking the commencement of the third and marginal region of the 
valvular flap are four bicellular hairs (s4). These are quite simple tapering 
hairs, the basal cells of each being an outgrowth of one of the epidermal 
cells of the valve. The distal portion tapers gradually to a point. These 
hairs are the only sensory hairs and upon stimulus cause the bladder to 
respond. Situated near the sensory hairs are three or four peculiar club- 
shaped hairs, which are not noticeable from the fact that the terminal cell of 
each is larger than usual and is almost spherical (fig. 3,6). Other elub-shaped 
hairs occur near by, but more exteriorly, and these are not so large or 
spherical distally. 
From the region enclosed by the four sensory hairs, and appearing to 
radiate outwards to the tree margin of the valve, are specialized cells which 
I consider as the principal motor tissue (fig. 6,mt). These cells are slightly . 
thicker-walled than other cells of the valve, and they have many projecting 
ridges from their walls internally. Other cells of the valve belonging to the 
middle region, as already seen, show similar thickenings, but by no means to 
such an extent as in the present region. 
The free edge of the valve fits into a slight groove along the anterior 
margin of the zone of specialized collar cells (fig. 5,4). This groove is as 
deep as the middle layer (fig. 5, md) of the collar zone. After action the 
valve always springs back, and its edge is held in this slight groove. A certain 
amount of mucus is secreted (fig. 5,m) apparently by the middle layer, and 
this makes complete a watertight fitting of the valve. The mucus is easily 
demonstrated in sections if the bladders have been fixed in Bouin’s Picro- 
formol. In the process of imbedding and staining, all pierie acid is washed 
out, but the mucus above-mentioned retains a conspicuous yellow or orange 
colour to the last, and is well seen in a preparation stained with heematoxy lin. 
It is seen to extend also for some distance along the middle layer of cells. 
From the two dorsal “corners” of the rim arise long, branched, antenna- 
like processes (fig. 1,ant.). These plumose antennæ bend downwards and 
outwards. Laterally, from each side of the rim are about five simple 
