26 U. S. BUREAU OF FISHERIES 



The rearing of mussels in hatchery troughs was continued, but this 

 work was subordinate to the researches of Dr. M. M. Ellis, of the Uni- 

 versity of Missouri, special investigator at the Fairport laboratory 

 during the past summer. Doctor Ellis studied the elimination of the 

 parasitic period in the culture of fresh-water mussels and made very 

 material headway in this direction. He also definitely determined 

 the importance of the acid-alkali balance of the blood of the fish to 

 the glochidia encysted in its gills. This proved to be an important 

 factor in the cultivation of mussels without host fishes. This work 

 will be continued. 



Doctor Ellis also worked on the effect of light upon the glochidia 

 of mussels. He determined that the unfiltered, ultraviolet rays of 

 direct sunlight are quickly fatal to glochidia, and that if only partially 

 filtered the}* may cause disturbances seriously affecting the develop- 

 ment of the glochidia. Juvenile mussels also appear to be sensitive 

 to ultraviolet rays, which confirms the observation made by Dr. 

 A. D. Howard that a greater proportion of juvenile mussels survives 

 when they are shielded from light. 



TERRAPINS 



The experiments in diamond-back terrapin culture, which have 

 been conducted at the Beaufort (N. C.) biological station for a 

 number of years, were continued with success. More information 

 is being gained all the time relative to the requirements of the terra- 

 pins. One of the most important recent contributions, from an 

 economic standpoint, had to do with crowding, it having been shown 

 that many more terrapins than it was formerly thought advisable to 

 hold can be held in an inclosure when a supply of clean water is 

 available. Stagnant or dirty water is extremely detrimental, especi- 

 ally when the animals are crowded. This work is under the super- 

 vision of Dr. Samuel F. Hildebrand, and is in the immediate charge 

 of Charles Hatsel. 



The total number of terrapins removed from the egg beds during 

 the fall of 1925 was 2,968. The total number taken from the egg 

 beds in the fall of 1924 was 3,458. The main cause of the decrease 

 in the number of terrapins hatched in 1925 was the decline in the 

 number of eggs laid by the original breeders, some of which have been 

 at the station since 1902 and others since 1906. All of these were 

 mature when confined, and some of them, no doubt, were already 

 very old. It remains to be seen whether the decrease is due merely 

 to the normal yearly fluctuations that have taken place previously or 

 whether a permanent decline (possibly due to old age) in eggs and 

 young produced has set in. 



A cooperative arrangement has been entered into with the Fisheries 

 Commission Board of North Carolina for hatching and liberating 

 young terrapins with the view of restocking the sadly depleted State 

 waters. The Fisheries Commission Board has impounded 488 adult 

 terrapins at the biological station for breeding purposes, and is sup- 

 plying their food and a man to assist in feeding and otherwise taking 

 care of the terrapins. Arrangements have been made to build 

 another pound and to extend this work. 



