ORTMANN: A MONOGRAPH OF THE NAJADES OF PENNSYLVANIA 309 
Sterki decided this question by investigating the sexual glands. Since I have 
found that the sex of any individual may be determined by an examination of the 
gills, it should be possible, to recognize hermaphroditism by the structure of the 
latter, for in the case of hermaphroditism no individual should be found exhibiting 
the male structure of the gills. 
This is indeed true, and I am not only able to confirm Sterki’s observation 
with reference to Anodonta imbecillis, but in addition I think I have discovered 
among the Pennsylvanian species in Symphynota compressa and S. viridis, two 
other cases in which hermaphroditism is at least the normal condition. The par- 
ticulars are as follows: 
Of Anodonta imbecillis, until toward the end of the summer of 1909, I found 
only 6 specimens (in May and beginning of June), every one gravid. On September 
14, 1909, I collected a large number (about thirty) of this species in the outlet of 
Lake Leboeuf, which again were all gravid with one exception, and the latter 
proved, upon anatomical examination, to be also an individual with the female 
structure of the gills. At that time, I was aware of the existence of this question, 
and was looking out for males, but was unable to find any. In 1910 I collected 
only a single individual, but again a gravid specimen. 
In the case of Symphynota compressa my observations are not so positive, and 
only during 1909 and 1910 did I pay attention to this species with this point in 
view. I repeatedly collected specimens, which were not gravid, in May, June, 
July, and the beginning of August; but these might have been sterile females as 
well as males. I also collected four specimens, not gravid, on October 10, 1907 
(together with gravid specimens). Of these I preserved two, believing them to be 
males; but upon investigation they proved to possess the female type of gills. 
During the month of September of 1908 I collected about twenty-five specimens, 
and among them there was not a single one which was not gravid. On August 18, 
1909, I found about twenty specimens at one locality, and on September 27, 1909, 
about fifteen at another place. On these occasions I was hunting for males, but 
was unable to find any. On the latter date I found four very young specimens, 
which were not gravid. Three of these were preserved, but they also had the 
female gill-structure. In 1910 the result was the same. Of three specimens found 
every one had the female structure, or was gravid. However, from Professor 
Charles Brookover in Akron, Ohio, I received a specimen of S. compressa coming 
from Lake Erie, at Cedar Point, Ohio, which had the male anatomy of the gills. 
This is indeed very remarkable in view of the fact, that among all the specimens 
collected in Pennsylvania and preserved in alcohol or examined on the spot, there 
was not a single male, and that I was altogether unable to find a male in our state. 
