the field. Various tissues of eight of these oysters were preserved in Bouin-3 solution, 

 and processed later in the la'boratory at Woods Hole. The processing, including paraffin 

 imljedding, sectioning, and staining was skillfully performed ty Eugenia Galtsoff , former 

 associate in zoology in George Washington University, whose assista^ice and cooperation 

 are here gratefully acknowledged. 



The purpose of the microscopic examination was twofoldi a) to determine the 

 existence of any identifiable pathological condition in the tissues, and "b) to find out 

 whether the oysters were infested hy parasites. Particular attention was paid to the 

 presence of spores of Hematopsis , a common gregarine parasite of the edi'ble oysters of 

 Middle Atlantic and South Atlantic- waters of the United States; to the infestation of 

 gonads tyy Bucephalus, a trematode worm which destroys the fertility of edi'ble oystersi 

 and to the occurrence of any other parasitic or commensal organisms v/hich may te detri- 

 mental to pearl oyster. Examinations of fresh material were made Isy tearing out small 

 pieces of organs, pressing them under a coverslip, and inspecting then at magnifications 

 of T 250 and X 625. The use of neutral red, methylene hlue, and other vital dyes was very 

 helpful in producing differential staining. Imhedded and sectioned material was stained 

 with haematoxylin and eosin. The results were negative. All the oysters examined appeared 

 to he in every respect normal and devoid of disease. E'er-.atopsls and Bucephalus were ahsentj 

 and no other suspicious organisms were found In the tissues, hlood, shell liquor, or 

 attached to the inner side of valves. Mud hlisters caused "oy tube forming amielids were 

 found rarely. 



The shells of live oysters were not infested hy the horing sponge, which, however, 

 was frequently found in old dead shells. A few specimens were found hored hy Lithophaga , 

 hut the infestation was nild, and the holes did not penetrate the entire thickness of 

 valves. The only commensal organism found in all pearl oysters was the shrimp Pontonia 

 pim^ae Lockington, which apparently has no ajiverse effect on its host. This shrimp occurs 

 in hoth Pinctada mazatlaaica and Pinna lanceolata , alvja"s confined to the cloaca. Each of 

 the oysters I examined }iarhored two Pontoniae. The shrinp nay he trouhlesome, for it 

 painfully pinches the fingers of the person opening the oyster. Local fishermen helieve 

 Pontonia is the male of the oyster, and in some mysterious way is concerned with fertiliza- 

 tion of female pearl oysters. 



Prom the results of microscopic examination, I conclude that all live oysters I 

 examined v;ere in healthy condition and had no recognizahle symptoms of any disease, 

 malnutrition, or poisoning. They v;ere free of parasites. 



Sex ratio and ripeness of the gonads 



Of the 27 live adult oysters the sex of which was examined in the field, ih were 

 females (U of them spawned out) , 10 were males, and the sex of the remaining three was not 

 recognizahle hecause of the indifferent stage of their gonads. At Station 6 (isla de Mina) 

 and Station 26 (Canal de Entro, Bahia Honda), attempts were made to fertilize the eggs. 

 Small pieces of gonads of ripe females were teased in a finger fowl filled with sea water, 

 and a small quantity of sperm suspension was added. Pinger howls were left on the tahle on 

 deck, protected against direct sunlight. The temperature of the water in the howls rose to 

 32.5° C. Samples of water with eggs were pipetted and examined under the microscope every 

 30 minutes for 6 hoiirs. There was no fertilization of eggs. The eggs were left overnight 

 and examined again. Hone showed a fertilization memhrane, arid there was no cleavage. At 

 the end of. the ohservation, the pH of the v/ater in the howls was 7*8. Pailure of the 

 fertilization test was a great disappointment, for the eggs appeared to he normal and in 

 excellent condition. Tie sperm, however, remained immohile. One mast rememher, however, 

 that the conditions under which the tests were made were unfavorahle. The water in the 

 howls was too warm as compared with the temperature of the sea (26.2" C. at«Station 6, and 

 29.5° C. at Station 26), and was continually agitated hy the movement of the ship. It is 

 impossihle to state, however, whether the failure of fertilization was due to these con- 

 ditions, or to some deficiency in sperm, which remained immohile in spite of the addition 

 of fresh sea water. In the edihle oyster, the motility of spermatozoa can he initiated 

 easily hy adding fresh sea water to the suspension of sperm. 



U2 



