PROGRESS IN BIOLOGICAL INQUIRIES, 1937 49 



mature spore (length 20;U, diameter lljx) contains a single vermi- 

 form sporozoite folded twice on itself and is the resting or final 

 developmental stage in the oyster. 



Under natural and laboratory conditions the hatching of the spores 

 takes ])lace in the intestine of the common mud crabs, Panopeus 

 herhsti and Eurypanopeus depressiis after these hosts have fed on 

 infected oyster meats. After undergoing a cycle of development in 

 the crustacean host, the parasite reaches an infective or gymnospore 

 stage, which is released into the water and may be carried within 

 the shell of the oyster by the feeding current. 



Experiments with vitally stained gymnospores show^ that they at- 

 tach to and penetrate the epithelium of the oyster gill by means of 

 a pseudopod projected from the central cell. Later stages may be 

 picked up by phagocytes and transported in the circulatory system 

 to nearly all parts of the body. With the formation of heavy, double- 

 walled sporocysts, the parasite has reached the characteristic resting 

 or dissemination stage commonly found in Ostvea vlrginica and var- 

 ious other members of the same class of mollusks. Further details 

 of the life history of this sporozoan will be published shortly in a 

 scientific journal. 



Studies of the effect of the parasite on adult oysters were conducted 

 in the laboratory where heavy infections could be produced. In bulk 

 experiments with several hundred oysters, losses of 66 to 73 percent 

 resulted over a period of 3 months. Kymograph records of shell 

 movement of heavily infected oysters showed abnormal and fre- 

 quent contractions of the adductor muscle followed by loss of holding 

 power and death of the mollusks. The injury to the oyster host may be 

 due to a toxin given off by the developing sporozoites, particularly 

 in the sensitive mantle tissue, or to actual physical obstruction of 

 the circulation by the masses of enlarged, infected phagocytes found 

 in the blood vessels of the gills and muscle. 



Practical prevention of the infection of oysters by this parasite is 

 possible by control of the primary hosts, the mud crabs. The crabs 

 do not migrate and can easily be removed, before the beds are planted, 

 by the use of dredges or scrapes equipped with fine mesh bags. The 

 possibility of destroying the crabs by chemicals such as copper salts, 

 chlorines, etc., is at present under investigation. 



Investigations in Flonda. — An experimental study of spawning 

 and setting of oysters in Apalachicola Bay, Fla., was begun early 

 in the spring by Dr. A. E. Hopkins. Because of the warm winter 

 many oysters retained fully matured eggs or sperms in the gonads. 

 Of samples taken early in March from St. Vincent Sound and Indian 

 Lagoon, about half were mature. In the eastern portion of the bay, 

 where the most extensive natural bars are located, only an occ{isional 

 sexually mature individual was found. A month later, in early April, 

 almost all specimens contained mature sex products. However, there 

 was no indication of spawning until the end of April and the first of 

 May, although for sometime previously the water temperature had 

 been in general above 20° C. Spawning did not occur throughout the 

 entire population at once but apparently involved only a small num- 

 ber of individuals at a time. A scattered set of seeds was obtained 

 on bags of shells beginning at the end of May and continuing 

 throughout the summer. 



