The American Midland Naturalist 
PUBLISHED BI-MONTHLY BY THE UNIVERSITY 
OF NOTRE DAME, NOTRE DAME, INDIANA 
VOL. VIII. JULY-SEPTEMBER, 1922. NOS. 4; 5- 
The Histological Structure of the Gills of the Najades with Special 
Reference to the Histology of the Groove Along the Edge of 
the Inner Gill. 
HIRAM J. BUSH. 
I—INTRODUCTORY 
The primary purpose of the investigation here recorded has 
been to determine the histological structure of the gill of the 
Najades with special reference to the groove along the ven- 
tral edge of the inner gill. It was at first intended to investi- 
gate the groove with the view of ascertaining its function. 
After some ‘work was done along this line it was found that 
Allen in a recent paper (2) (1921) had investigated the prob- 
lem very thoroughly and arrived. at conclusions’ which the 
present work corroborated in so far as it had been completed, 
namely that the function of the groove is to act as a channel 
for conveying food to the labial palps. The first mention of 
this problem so far as the author is aware is by Dr. Arnold 
1. Ortmann of the staff of the Carnegie Museum in his Mono- 
graph of the Najades of Pennsylvania (4). On page 294 of 
that publication he says, “Making cross sections through the 
gills we observe that the outer edge of the outer gill is simply 
rounded off, while i in. the inner gill a peculiar longitudinal fur- 
row extends along its edge, which may be seen microscop- 
ically. As to the meaning of the furrow, I can not make any 
Suggestion and am only able to state the fact of its presence. 
By the presence of this furrow an inner may always be distin- 
guished from an outer gill.” 
