308 MEMOIRS OF THE CARNEGIE MUSEUM 
collected June 27, had most of the placents discharged, but of the remaining 
few, some were protruding from the edge of the gill, exactly as described above. 
Females, discharging glochidia, and with openings in the edge of the marsupium, 
were seen in the following additional cases: Lampsilis luteola, May 6 and July 
7 (on the latter date in several individuals); Lampsilis ventricosa, May 21 and 
June 23; Lampsilis multiradiata, June 23. 
To all appearance, these holes are present only during the actual discharge 
of the placente or the glochidia, and immediately after it, and close up again 
very soon, so that it is difficult in sectioning, to strike just the right point of the 
edge of the gill, where they are best visible, and this may account for my failure 
to obtain a greater number of good slides. It also should be remembered, that 
gravid females in the act of discharging, are naturally searce among material, which 
was not collected with this question in view, and it is indeed astonishing, that I 
found so many instances supporting the assumption, that in the Lampsilis-group, 
that is to say, in those forms, in which the edge of the marsupium bulges out 
beyond the original marginal line of the gill, the glochidia are discharged, not by 
way of the natural outlets, but by breaking through the marginal wall of the gill. 
If this is so, a very important correlation is suggested: the anatomical peculiarities 
of the edge of the marsupium in these forms appear as a direct adaptation to the 
way of discharging the glochidia: the edge of the marsupium is built for this purpose. 
Nevertheless this phenomenon should be further studied. I have given here 
my observations, and I think they are correct and conclusive, for I cannot imagine 
that conditions as represented in the figures 18 and 20 on Plate LXXXVIII are 
wholly artificial and abnormal. 
From the above instances we see, as well as from some of the older observations 
of Lea, that in some cases the whole placentz are discharged, in others free glochi- 
dia. This is connected with the greater or lesser solidity of the placentz (See 
above, p. 298), but its systematic value is not very great; at any rate, each one of 
the greater groups contains examples of either method of discharge. 
D. HERMAPHRODITISM. 
Lea and others have demonstrated that most of our Unionide are gonochorists, 
and the existence of hermaphrodites remained doubtful, till Sterki found them. 
In a number of cases, hermaphroditism is occasional and exceptional, according 
to Sterki (1898, p. 30), and he names the following instances: Quadrula rubiginosa, 
Q. pryamidata, Lampsilis parva. But in another ease, that of Anodonta imbecillis 
(Nautilus, 12, 1898, p. 87), he found that hermaphroditism is the normal condition. 
