experiments on supposedly similar organs in other forms. The 

 scallop normally lies on the right shell valve, but I am not sure 

 that it makes any particular effort to turn over when it is placed 

 on the other valve. When it swims and settles to the bottom, 

 it settles uniformly on the right valve. Whether this is due to 

 the shape of the shell or to some determining factor outside of 

 the nervous system of the scallop or not, is not known. 



EMBRYOLOGY. 



From observations made early in the summer, it seemed prob- 

 able that the giant scallop spawned rather late in the season ; 

 accordingly as soon as other duties permitted, August 20, 1901, 

 quarters were procured at Bass Harbor, Mt. Desert Island, 

 Maine, and work begun. Examination of specimens showed 

 that for the most part they had not spawned, and that sperma- 

 toza removed from the testis and placed in sea water were 

 active. Many trials were made while at Bass Harbor to arti- 

 ficially fertilize the eggs by cutting them out and mixing them 

 with sea water containing sperm which had likewise been pro- 

 cured by cutting. Very few of the eggs showed any signs of 

 development, and most of them that started did not develop nor- 

 mally. Eggs thus removed from a lamellibranch are irregular 

 in shape, due no doubt to their crowded condition in the ovaries. 

 For some reason that is not understood, the eggs of many species 

 of lamellibranchs seldom round up. are incapable of fertiliza- 

 tion, and soon go to pieces when they are cut out of the ovary. 

 Such is the case with this form. Eggs removed even during 

 the height of the breeding season did not develop well. 



It was found that scallops that were full of eggs and sperm 

 when placed in a floating car on August 23rd, had, when exam- 

 ined the next day, thrown most of their sexual products. Speci- 

 mens had also been placed in large vessels of water at the same 

 time, but these had not spawned and did not spawn although 

 kept another day. The animals die rapidly in such vessels of 

 water, seldom living more than three days, and frequently not 

 more than one. A careful watch indicated that specimens put in 

 the car did not spawn during the middle part of the day, so night 

 observations were made. Fresh specimens were placed in the 



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