16 



the anus with the stomach lengthens and becomes the intestine. 

 This part of the digestive tract soon becomes very much bent, 

 upon itself, so that its length is several times the distance be- 

 tween the stomach and anus. The two sides of the stomach 

 become folded off to form the two halves of the liver, which 

 later fuse into one indistinguishable mass. 



Up to the time of the formation of the permanent mouth, 

 the embryo had developed without any increase in size, but after 

 the establishment of the two openings to the digestive tract, food 

 is taken and an increase in size takes place rapidly. 



When the embryo settles down to its fixed existence, the 

 mantle on the left side extends beyond the edge of the shell 

 and secretes a layer of the same material, which attaches it to- 

 the permanent support. 



The velum is resorbed and the organs of the body assume 

 the proportions characteristic of the adult. 



The great practical utility of a knowledge of the develop- 

 ment of the oyster, is in that it shows the vast number of em- 

 bryos that are formed at each breeding season, and suggest'i 

 the feasibility of adopting the method of exposing some hard 

 bodies on which the young may settle when they have become 

 old enough to give up their free-swimming existence. 



PHYSICAL AND BIOLOGICAL CONDITIONS ON OYSTER 

 BEDS— TEMPERATURE OF THE WATER. 



Oysters live in water of very different temperatures, both- 

 r.s to the average for the year, and the extremes met at different 

 reasons. In the Louisiana fields, the extremes met with are not 

 likely to vary from more than 45 degrees (Fahrenheit) as tho- 

 lowest to 75 or 80 degrees as the highest. This upper limit 

 may be exceeded in some places, where the water is very shallow, 

 during the warmest months of the summer, while in unusually 

 severe weather in wiiiter the temperature may fall nearly to- 

 the freezing point in the same lo'calities. 



The temperature has an important bearing on the" food 

 supply of the oysters. When the water is warm, there is a 

 rapid multiplication of the small plants on which the oysters 

 feed, and at the same time the vital activities of the oyster 

 are quickened, so that the growth is most rapid in the warmer- 

 seasons. 



