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. It is 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 fiuviatilis 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 to 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 a short tube with open end, through which 

 (according to Barry) the spermatozoa enter. The ova pass out of 



