ZOOLOGY. 347 



maphrodite, while in others the sexes may be separate. If the affirmative 

 of this question be established, some other cause for the occurrence of 

 the two forms of shells must be sought. It would, however, be an 

 anomaly in nature, if one half of the individuals should prove barren, 

 and of no use whatever, in a family where she has provided so care- 

 fully for the increase and perpetuity of the species. So prolific, indeed, 

 are fertile individuals, that they produce annually their young in num- 

 bers almost too great to admit of enumeration. Mr. Lea calculated 

 the oviducts of an Anodonta undulata to contain 600,000 young shells. 

 This, it will be recollected, is a small species, and does not produce a 

 tithe of the young contained in a prolific Anodonta plana. The barren 

 members of a colony of honey-bees, (the Apis mellifica,) might, at 

 first view, seem to afford an analogy ; but they subserve a useful pur- 

 pose. On the products of their labor are sustained all the members 

 of their community. If the barren mollusci do not fulfil the purposes of 

 the male, it is difficult to discover of what use they are in creation. 

 It may be proper to state a fact in regard to the habits of the U. gib- 

 bosa, and its allied species, the Unio rangianus, which may have some 

 connection with the subject before us. During the months of April 

 or May, according to the state of water in the streams, and warmth 

 of the weather, the females may be seen lying upon their beaks on 

 gravelly ripples, with their heads directed up stream, and the valves of 

 their shells extended to their utmost capacity. At this time they are 

 heavy with their young. The pure whiteness of their bodies and 

 appendages renders them conspicuous objects, seen through the limpid 

 water ; and their position and appearance would lead to the conclu- 

 sion that they were dead, and the valves were expanding as their trans- 

 verse muscles were relaxed. An attempt at taking a specimen into 

 the hand will at once show that it still abounds in vitality. The 

 object of assuming this position at this particular period of the year, I 

 could never discover, but suspect it to have some connection with the 

 process of fecundation. In the immediate vicinity are always found 

 more or less males ; but as their shells remain closed, they are not so 

 readily recognized. The female, U. vcntricosus and fasciolus, may 

 sometimes be seen throwing out of their shells the prolongations of 

 their mantles, and playing them about the water, during clear and 

 warm days in autumn. At the same time male individuals may 

 always be found very contiguous, and it has often been observed by 

 collectors, that, at this season, these species seem to be associated in 

 pairs. 



On several occasions I have seen the females of various species of 

 these mollusci discharging their young progeny. At that period of ex- 

 istence they are perfectly formed shells, as may be discovered by the 

 naked eye, if they are placed in the sun for an hour; or by the aid of 

 a microscope when first obtained. They are agglutinated together with 

 a secretion, probably of mucus and albumen ; and the mass conforms 

 to the shape and size of the branchial cell. The contents of one cell 

 are thrown off at a time, fry a jet of water, issuing rapidly through a 

 syphon or contracted aperture, formed by the posterior margins of the 

 mantle. The mass, on being evacuated,* falls upon the bottom of the 



