50 INLAND FISHEKIES. 



the time tliey are 48 hours old the shells are formed with a shape 

 characteristic of the scallops and disting-uishiuo- them from other 

 shell-fish in the corresponding- stages of development. 



How long- the scallop remains in the swimming stage is not 

 known. There are obvious difficulties in the way of confining 

 such minute and active creatures, and at the same time giving 

 them a free circulation of water. 



They were kept for four days, however, in the swimming condi- 

 tion, and it is hoped that during the next summer the duration of 

 the free-swimming period may be ascertained. 



5. What are the habits of the young scallops after they have set f 

 — The actual changes undergone when the swimming "larvae" 

 sets and becomes attached to the eel-grass, sea-weed, etc., awaits 

 investigation. The setting doubtless occurs from June 1 to July 

 1, when the young are still of microscopic size. Throughout 

 xlugust and even in September the newly set scallops may be 

 found in the eel-grass attached to the grass or sea- weed by byssus 

 threads like those which are spun by the mussels and the young 

 of the soft clam. 



6. What is the rate of growth under natural conditions ? — This 

 problem has received a good share of attention because of its 

 economic as well as biological intei'est, and also because the 

 opportunities for solving it were, at Wickford, exceptionally 'favor- 

 able. The systematic observations on the rate of growth were 

 begun in October, 1899, on the set of the previous June, and have 

 been continued up to January, 1900. The record, therefore, covers 

 the period from the 4th to the 18th month of the life of the 1899 

 scallops. 



The method employed is as follows. A large number (200-1,000) 

 of specimens were taken at intervals, usually of about a month, and 

 carefully measured with calipers, and the average size obtained 

 for each date. 



This method is satisfactory and gives a faithful record of the 

 growth because there is only a comparatively slight variation in the 

 size of the individuals of the same set at any one time. For in- 



