GERM-CELL HISTORY IN THE BROOK LAMPREY 9 



tissues of the body. Metamorphosis seems to be the beginning 

 of the death process, since at this time the intestine and the 

 portal vein degenerate, thus making it impossible for the ani- 

 mal to feed again. The metabolic processes taking place in the 

 adult must be concerned largely with material already present 

 in the body at the time of metamorphosis. It is not unlikely, 

 however, that water and some nutritive substances may be 

 absorbed during adult life through the external surface of the 

 body. Putter ('09) found that sea-water and probably also 

 fresh water contains amino-acids, oils, and carbohydrates, and 

 that many aquatic animals absorb nutrition from solution, thus 

 rendering them only in part dependent upon plankton. Alcock 

 ('99) found that the larvae of the lamprey secrete an enzyme 

 through the skin which has some digestive action on bacteria 

 that might attack them in their burrows. This renders it prob- 

 able that some food may be absorbed through the skin of the 

 larvae and perhaps of the adult. 



MATERIALS AND METHODS 



Adults have been obtained at all seasons of the year except 

 during the three months following the spawning -period, but only 

 those taken during the spawning season contained fully matured 

 sex cells. In the laboratory the adults must be kept in running 

 water, but the larvae live for months in standing tap-water if 

 it be kept cool. Early larval stages are best obtained from 

 artificially fertilized eggs. The largest percentage of fertiliza- 

 tion is had from eggs of females taken at the height of the spawn- 

 ing season and used at once. The fertilized eggs are placed in 

 tap-water in covered bacteria dishes and require no more care 

 than an occasional change of water, which should be made 

 without considerable change of temperature. Larvae from such 

 eggs have been kept without much difficulty in the same dishes 

 for as long as forty days, i.e., until most of the yolk is absorbed. 

 Older larvae were obtained from the brook at all seasons and for 

 a period of about four years. 



By recording the moment of fertilization and by watching 

 the progress of development, it was possible to obtain any 



