PIIYLOGENY OF THE PELECYPODA. 287 



service in eating vegetable growth on the glass, that would have been injurious to the 

 young oysters and other fixed forms, which I was studying. 



The following free Pelecypods were also caught in the pipes as entrapped forms; 

 many specimens of young Mija arenaria, L., varying from 0.5 mm. to 6 mm. in length, 

 and very young Venus mercenaria, L., 0.5 mm. to 2 mm. in length. Aryiria pexata 

 appears again under this list of entrapped forms, as I found a very young specimen 

 0.75 mm. long which was free. Pecten irradians also belongs to both the lists of free 

 and attached forms, a numl)er of unattached individuals varying 'from 0.75 mm. to 1.5 

 mm. in height being secured. It is a stage of development preceding the attached bys- 

 sated stage as described in the text. Occasionally adult Pectens and Lcevicardlum 

 moi'toni, Perkins, were entrapped. 



A bottle, bearing many oyster spats and Anomias, was washed up on the shore dur- 

 ing a storm, showing that they may be caught on glass under other conditions than those 

 afforded by the drain-pipes. Probably the oysters set in the bottle when it was in com- 

 paratively deep water, where moderate quiet prevailed. 



The nature of my researches was such that young oysters with shells as clean and 

 perfectly presei'ved as possible were desired. Year-old oysters perfectly cleaned were 

 found very beautifully pi-eserved in the inside whorls of a dead Sycotopus shell, where 

 they were completely protected from all eroding action. To imitate these conditions, in 

 the salt-pond above referred to, a large number of inverted flower-pots, two-and-a-half 

 and three inches in diameter, were suspended from galvanized wire stretched between 

 stakes di'iven firmly into the sand. The pots were raised about six inches from the sand. 

 This met with entire success, the pots in many instances being almost literally covered 

 with spat. On the outside of the pots very little, and on the inside no sediment was de- 

 posited, as the pots hung like suspended bell-jars, so that the oysters were clean and well 

 preserved. Further, on account of the porosity of the earthenware, the oysters had less 

 hold than on natiu'al cultch of stones and shells, and were easily I'emoved for study. 

 The owner of the pond in the winter of 1887 built a dam across the entrance so as to hold 

 about two feet of water in the pond. Under these changed conditions, inverted pots 

 were again suspended on the 17th of July, 1888. Oysters set on pots quite as suc- 

 cessfully as in 1887, when the pots were exposed at low tide, and they grew much 

 more rapidly. 



In four large inverted pots microscope slide boxes filled with slides were suspended. 

 The boxes were strengthened by brass nails, as they were simply glued and would have 

 fallen apail in the water. One hundred slides were thus exposed in an horizontal posi- 

 tion, but they were not as successful as glass exposed in the drain-pipes. They became 

 coated with sediment on their upper faces and covered with minute vegetable and animal 

 growths on their lower faces. The last is ascribed to the fact that the slides were so 

 close to one another that the scavenger gasteropods, Littorina and Ilyanassa, could not 

 get at them and destroy the objectionable growths as they did in the loosely-filled drain 

 pipes. 



In 1887, a number of wooden plates, such as are used at picnics, were exposed in the 

 salt-pond. Holes were punched in the plates which were then strung on galvanized iron 



