116 COMMISSION OF CONSERVATION 



In 1908 he again proposed the question: 



"What is the length of the free-swimming life of the oyster fry? The 



answer was left in a state of uncertainty, so we were anxious to decisively solve this 

 problem during the present year, and we accordingly made it the primary quest of our 

 experiments We found the length of time which elapses between spawn- 

 ing and spatting to depend somewhat on the temperature of the water. At a tempera- 

 ture ranging between 70 and 75 degrees Fahrenheit, the fry required about three 

 weeks to mature to the spatting stage. At a temperature ranging from 75 to 80 de- 

 grees the period is only two weeks." 



In the same year he began to distinguish "small," "medium," and 

 "large" larvce, and stated that: 



" When it is ready to set as spat it has grown more than sixty fold in bulk, and at- 

 tained nearly a hundredth of an inch in length." 



It will be clear that Nelson's views varied from year to year, and 

 that such statements as those made in 1901 (p. 322): "The bottom and 

 sides of several of the tumblers were covered with spat in the first shell 

 stage," and 1902 (p. 336): "We occasionally secured a complete develop- 

 ment of the fry up to the spat stage," were mistakes of the same nature 

 as those of Rice and Ryder. These were not true fixations but accidental 

 or abnormal temporary attachments of straight-hinge stages. Nelson's 

 first correct understanding of the full-grown larva dates from 1907, when 

 he made numerous, laborious filtrations of sea-water and examined the 

 residue with a microscope. 



