i68 



BULLETIN OF THE BUREAU OF FISHERIES. 



A few typical cases, selected from our records of infections are given in the accom- 

 panying table, which illustrates the far greater variability in the parasitic period than 

 that observed by Harms. 



Table Showing Infections with Glochidia. 



In the case of Symphynota complanata, which has hooked glochidia essentially like 

 those of Anodonia, the period varied from 9 to i8 days at average temperatures of 17.8° 

 to 16° C, as compared with Harms's 21 days at practically the same temperature. 

 At lower temperatures, about 10°, we have recorded a period of 74 days for S. costata. 



The absence of a close correspondence between the temperature and the duration 

 of the parasitism has been much more conspicuous in the case of bookless glochidia, which 

 have shown not only a remarkable range in the period but a considerable irregularity in dif- 

 ferent experiments made at about the same temperature. The shortest period recorded 

 by us was seven days in an infection of black bass with the glochidia of Lampsilis sub- 

 rostrata and L. recta in April when the average temperature during the parasitism was 

 20.5°, but this unusual time was only observed in this one instance. A still more 

 remarkable case, but at the opposite extreme, was an infection of black bass and crappie 

 with the glochidia of L. ligamentina and L. recta which remained on the fish for 13 to 16 

 weeks. The infection was made in November and the young mussels were liberated 

 during a period of about three weeks in the following Febniary and March; during the 

 parasitism the temperature varied from about 16° to 18. ° The cause of the extreme 

 duration in this case is not known, for in no other experiment at the same temperature 

 has the parasitism lasted for more than 25 days. 



