100 THE AMERICAN MIDLAND NATURALIST 
number of short rods overlapping at the ends. This construc- 
tion gives the.gill far more flexibility than it would have if 
the rods were a single rigid piece. However in his drawings, 
Peck places the rods out near the end of the filament while I 
have found them in the Najades to occur near the base of the 
filament where it joins the interfilamenter junction. In the 
structure they also differ; Peck shows them as cylinders (cir- 
cular in cross-section) while in the Najades they are greatly 
flattened so as to resemble a knife blade with the edge per- 
pendicular to the surface of the lamella. These differences are 
shown in figures 5 and 6. 
The connective tissue which underlays the ciliated epithe-- 
lium corresponds to areolar connective tissue. When exam- 
ined under the microscope it is seen to be made up of very 
fine, transparent white fibers. It is very scant in thickness, 
but runs along the entire lamella underneath the epithelium, 
as well as under the cells lining the water tubes, only being 
interrupted at the ostia, where the bundle of fibers divides and 
encircles the opening. The connective tissue is shown in figure 
a conn. tv.) ; 
The tissue filling up the space inside the filaments as well 
as the interfilamentar junctions is in the form of a reticulum. 
The cells are stellate in form and have long branching pro- 
cesses of cytoplasm which interlace with each other and even - 
appear to fuse at times with those of other cells: The nuclei 
of these cells vary from the extreme elliptical to the circular 
in shape but are usually in the form of an ellipse with the 
short axis about two-thirds of the length of the long axis. 
The size of these nuclei varies around one to three microns in 
diameter. The processes of the cytoplasm weave around one 
another so much that their length cannot be determined, how- 
ever I have frequently seen a single strand extending across 
the entire width of the lamella. The tissue resembles in ap- 
pearance the mesenchymal cells in primitive mesoblastic tis- 
sue. Large blood vessels run through this tissue and some of 
the smaller vessels open into it. This reticulum thus acts as 
a blood sinus. The circulation in the gills thus can hardly be 
called a closed system. Since this reticulum extends out into 
the filaments the animal is rendered partly independent of 
