OF MASSACHUSETTS. 



133 



restriction of the water circulation by the clogging of the fine meshes 

 by plant growth. This was avoided as much as possible in the growth 

 experiments by frequently cleaning the cages, and transferring the 

 small scallops as soon as their size permitted to the larger cages. In 

 spite of this care the growth of the " seed " inside the cages proved 

 less than those attached outside. Old scallops, as well as, young, were 

 confined in the baskets for growth records. 



The Biological Raft. The raft (Fig. 79) from which the wire 

 baskets were suspended proved particularly useful in the study of the 

 post-embryonic life history of the scallop, which " set " in numbers 

 on the boxes, wire cages and ropes, where specimens could be obtained 

 in all stages of development for laboratory examination. From the 

 raft at various depths were suspended wire cages and boxes, in which 

 growth experiments upon the quahaug, clam and scallop were con- 

 ducted. The raft, 20 feet long by 10 feet wide, was made of two 4 

 by 6 inch beams, 20 feet long, which were held in place by cross beams, 

 3 by 4 inches in size. On the framework was a floor, except for a 

 large central " well." Four trapdoors led to smaller " wells " on each 

 side. The raft was buoyed by six oil barrels, two on each end and 

 two on the sides, and was moored in the Powder Hole in 20 feet of 

 water. The scheme of box spat collecting from a raft is recommended 

 to biological students, as the young of many worms, crustaceans, mol- 

 lusks and other marine forms are caught easily in sand boxes. 



A. Life Table. 



