6 BULLETIN OF THE BUREAU OF FISHERIES 



effect of temperature on the activity of the gill. An effort was made to put the 

 experimental work on a quantitative basis and whenever possible to give an accurate 

 measurement of the reaction of the organism. The experiments were carried out at 

 the United States Fisheries Biological Station at Woods Hole, Mass., in the summers 

 of 1925 and 1926 and the winter of 1926, and in the Pease Laboratories in New York. 

 The author wishes to acknowledge his gratitude to Dr. H. D. Pease for extending the 

 privilege of using his laboratory and supplying technical assistance in several bac- 

 teriological experiments performed in connection with this investigation. 



The oysters used in the experiments were received from Long Island Sound, 

 Wellfleet Harbor, Mass., Wareham Kiver, Mass., and Chesapeake Bay. No differ- 

 ences in the behavior of oysters from these localities were noticed. 



STRUCTURE OF THE OYSTER GILL 



The gill of an oyster is a complex, cUiated organ that takes part in three impor- 

 tant functions of the organism — respiration, feeding, and excretion. One of its most 

 noticeable activities consists in producing a strong current of water, which passes 

 through numerous branchial chambers and insures the e.xchange of gases between 

 the tissues of the organism and the surrounding medium. The material suspended 

 in water and brought in with the current constitutes the food of the oyster. It settles 

 on the surface of the gill and, after being entangled in the mucus excreted by numerous 

 gland cells, is pushed by the ciliary epithelium toward the distal edges of the gill 

 laminiB and is conveyed to the labial palps, where it is either rejected or enters into 

 the digestive tract. When the oyster is aot feeding and keeps its valves closed the 

 gland cells of the gills continue to excrete mucus, which accumulates in a large quan- 

 tity on the surface of the gUls and is discharged into water at the first opportunity. 

 The structure of the lamellibranchiate gill has been the object of numerous investi- 

 gations, and for a detailed anatomical and histological description the reader is refer- 

 red to the works of Peck (1S77), KeUog (1S92), Janssens (1893), Eidewood (1903), 

 and Yonge (1926). It is necessary, however, for the purpose of the present paper, 

 to give a brief account of its essential features. 



The oyster has two gills, each formed by one outer and one inner demibranch. 

 In a transverse section the gill presents the figure of the letter W- Each demibranch 

 consists of one descending and one ascending lamella, leaving a space between them 

 and being united at their lower ends. The upper edges of the ascending lamellae of 

 the inner demibranchs are imited in the middle line, those of the outer are fused 

 with the mantle. The spaces above the gill lamella; are called epibranchial or supra- 

 branchial chambers; they open posteriorly into one large exhalant chamber (cloaca). 

 The spaces below the lamellae (so-called infrabranchial chambers) are completely 

 shut off from the epibranchial chambers, and communication between them is possible 

 only through numerous minute pores in the gill. 



The gill lamellae are made up of numerous parallel filaments (fig. l,fi.) arranged 

 in rows, alternatingly forming crests and grooves. There are from 10 to 16 filaments 

 to each crest. According to Herdmann (1899) there must be over 2,000 filaments 

 for each surface of each gill, or from.8,000 to 10,000 filaments in all. Due to the pecul- 

 iar arrangement of the filaments, the surface of the gill is plicate, the crests of the 



