78 BULLETIN OF THE BUREAU OF FISHERIES. 



sunk in a protected part of Lake Pepin. In the pen thus made it was possible to retain 

 a considerable number of fish carrying heavy infections. At the end of the season the 

 wooden bottom was floated to the surface, and an examination revealed a total of 1 1,000 

 small mussels as reported. This is to date the greatest quantity production of mussels 

 yet attained in an inclosure. This method has several obvious good features for situa- 

 tions in which it may be employed. It approaches natural conditions more closely 

 than the other methods described. The suitable depth for both fish and mussels is 

 more readily obtained than in a crate, as well as more ample range in other directions. 

 It seems doubtful if it can be used in a river where the current would remove the young 

 mussels or the silt deposit cover them too rapidly. 



This season (1920) a test of the device is being made in the growing of river mussels 

 in the Fox River, where the mucket mussel (Lampsilis ligamentind) is abundant and 

 apparently thriving, since young mussels are readily found. The water of this stream is 

 clear so large a part of the time that a protected location devoid of current should prove 

 suitable. It is difficult to see how such a pen could be employed in a turbid river like 

 the Mississippi, since at points devoid of current the precipitation of silt would bury the 

 young mussels. The habitat of juvenile mussels in the Mississippi has been found to 

 be a current-swept gravel bottom, always clean despite the almost constant presence 

 of mud-laden waters. 



STRUCTURE AND DEVELOPMENT OF JUVENILE MUSSELS. 



The rearing of these mussels through the juvenile stage presented for the first time 

 the opportunity to determine the structure at almost any age and processes of develop- 

 ment during this period in the life history of fresh-water mussels. The investigations by 

 Herbers (1913) and Harms (1909) have recounted in detail the development during that 

 period for the Anodontas, Margaritanas, and Unios. In these cases, however, the juve- 

 niles were obtained for the most part free in nature, and therefore their age could not 

 be given with certainty. As no detailed account has been published for the develop- 

 ment of the large and valuable group of mussels included under the Lampsilinae, the 

 description of complete development in these would be a distinct contribution to our 

 knowledge of mussels. However, because of other features demanding more attention 

 at the present time, the intention of this paper is to mention only a few prominent 

 points in the development, reserving the detailed account for another publication. 



Upon beginning free life the shell of the young mussel, as has been stated above, 

 is that of the larva. When closed, therefore, no striking difference between the young 

 mussel and the glochidium is noticeable. Like the glochidium, it is for the most part 

 colorless and transparent. If, however, the young mussel is alive it soon extends its 

 foot, and in its use quickly demonstrates it to be an organ well developed for the 

 purposes of locomotion. The foot is somewhat cleft at the apex, so as to give a bilobed 

 appearance, and is clothed with cilia, all of which are in rapid motion during extension. 

 On smooth surfaces like glass it has the power of adhesion, a property apparently not 

 held in the adult, at least not to the same extent. By means of this organ the young 

 mussel is able to move about rapidly. These peculiarities in the foot of the early juve- 

 nile are soon lost, and during the first month the foot assumes the characteristic form 

 of this organ in the adult. 



