90 American Fisheries Society 



donta cellensis, Schrot, while conducting studies on the 

 embryology of that musselLff 



The results in growth indicate that the method pro- 

 vides a close approach to a natural environment and thus 

 furnishes a means of readily following the life history. 

 In this way we have been able to determine features that 

 were not accurately known before. 



It is not my purpose here to take these up in detail but 

 we may indicate the events and their chronology up to 

 the second generation which may be considered a com- 

 pletion of the life cycle. Glochidia were taken May 21st 

 from the Lake Pepin mucket, Lampsilis luteola Lamarck, 

 and fish infected with them on this date. The parasitic 

 period lasted for 18 to 20 days or until June 9th, The 

 extensive and remarkable changes of this stage take place 

 in an even shorter time under some conditions. In this 

 species the mussel makes no increase in size during meta- 

 morphosis. Thus at the beginning of free life, it is very 

 small and becomes easily a prey to numerous enemies. 

 This period, therefore, is critical in the life of the mussel, 

 perhaps as much so as that of the larva. 



The period of development succeeding metamorphosis 

 from the beginning of free life up to the attainment of 

 the adult condition comprises what is called the juvenile 

 stage. The shell of juveniles, up to the second month, has 

 two features that are characteristic of this early period. 

 In consistency, it is like horn, being transparent and less 

 hard than later when it becomes calcareous. The surface 

 is usually uneven owing to a series of regular and rela- 

 tively high undulations, knobs, etc., which are character- 

 istic for each species. These are designated as "Um- 

 bonal sculptures" by conchologists in describing the adult 

 mussel, in which they are not infrequently found well 

 preserved. Another structure to which I wish to call 

 attention is the byssus, an organ that is characteristic of 

 the juvenile stage in certain groups of fresh-water mus- 

 sels. It consists of a hyaline thread produced by the 



•j-j-Herbers, Karl: 1913, Entwicklungsgeschichte von Anodonta cellensis 

 Schrot. Zeitschrift, Wiss. Zool. Bd. 108 Heft. 1. 



