190 THIRTY-FIFTH REPORT ON THE STATE MUSEUM. 
The non-glandular sac of the renal organ connects with the 
branchial chamber, is filled with water and carries off the waste pro- 
duct separated from the blood by the action of the glandular sac. 
SEX AND REPRODUCTION. 
Formerly the Anodonta was considered to be androgynous or uni- 
sexual, that is, the male and female organs combined in one animal. 
Leeuwenhoek, in 1702, maintained that they were bisexual, though 
afterward changing his opinion, ‘The former view is now accepted 
by nearly all writers on the subject, though it is still maintained by some 
that they are unisexual. The fact that the organs of generation in 
all individuals are very similar, and as far as my observation goes, dur- 
ing the breeding season fully nine-tenths of the animals have their gills 
distended with young, gives some plausibility to that belief, for if the 
animals are bisexual, we would naturally expect to find the sexes 
in about equal proportions. Itis claimed also that from the greater 
room required by the female in the shell, owing to the distension of the 
gills with the young, that the shells of that sex are more gibbous than 
those of the male, but so far as Anodonta fluviatilis is concerned, that 
belief is an error, though undoubtedly true in regard to some 
species of Unio. Among the few Anodonta found by me, the gills of 
which did not contain young, were some, the gibbosity of which was 
so great that the thickness was nearly equal tc the height, while among 
those, the gills of which did contain young, were some quite flat, the 
thickness scarcely exceeding one-fourth the height. That some of the 
animals were without young does not weaken the force of the argu- 
ment of those believing in unisexuality, for even if the animals were 
hermaphroditic, from various causes there would, in all probability, 
be some without young. It seems to me that the simplest way to set- 
tle the matter would be, not microscopic investigations, but to collect 
large numbers at the time when the gills of the females are distended 
with young, if half or even one-third were without young it would nearly 
prove the bisexual view to be right; on the other hand, if nearly all 
were with young, the opposite would be proved. For certainly in order 
to fertilize the individuals in a pond or river, the males should be in con- 
siderable numbers. The generative organs, testes and ovaries consist of 
racemose glands, situated on each side of the subhepatic region of the 
body, the external openings of which are near the attachment of the 
inner gill to the body by the side of the openings of the pleural sac of 
the renal organ. The egg is globular and transparent. The sperma- 
tozoa are short rod-like bodies, with an active cilium. The yolk of the 
egg is prolonged into ashort tube with open end, through which 
(according to Barry) the spermatozoa enter. The ova pass out of 
