Corwin. — Raising Freshwater Mussels 83 



November 10th, 1918. Although it was evident that but few, if 

 any, young mussels had been dropped in this pen before the 

 removal of the fishes, still the pen was resubmerged and left until 

 September of this year, when it was raised and examined. 



Seventy- two second season mussels were found. These showed 

 clearly the first season shell, which measured from 1.4 to 2.3 milli- 

 meters, beyond which extended the second year's growth. The 

 largest juvenile luteola from the Stockholm enclosure was 21.6 

 and the smallest 7.3 millimeters long. The average second 

 season's growth was 15.26 millimeters. 



1919 Enclosures 



The experimental work during the present season was conducted 

 so as to show the relation of the length of the parasitic period to 

 season and temperature of the water. The enclosures were con- 

 structed in two parts; a board bottom and a wire netting cage 

 resting upon it which could be raised when desired. In all, 14 

 such enclosures were employed. Infections were made at about 

 15-day intervals from May 20th to September 4th. Several 

 infections were made simultaneously in each of the three localities 

 previously mentioned. 



Generally speaking, it was found that glochidia placed on fish 

 up to the middle of July, that is, in spring and early summer 

 infections, required a shorter period for metamorphosis than 

 those used in infections after July, late summer and fall infections. 

 For instance, spawn placed on fish May 20th, dropped from the 

 host in from 26 to 29 days, when the water temperature was rising 

 from 60 to 78 degrees F. Spawn placed on fish June 5th dropped 

 off in from 18 to 20 days — water temperature 68 to 78 degrees F. 



Fishes infected July 1st, carried the young mussels from 14 to 68 

 days — water temperature falling 77 to 74 degrees F. 



A significant observation was made on the behavior of old 

 glochidia, that is, those which had been carried by the parent 

 over the winter and spring; and new glochidia, that is, mature 

 ones of the present season. On July 17th, two lots of fishes of 

 the same species were infected and kept in separate but adjacent 

 pens. The first lot was infected with old glochidia; the second lot 

 was infected with glochidia of the present season. The first lot 

 had completely dropped the young mussels within 14 days. Some 



