418 E. J. ALLEN AND E. W. NELSON. 



liability to putrefy. After an interval of ten or fifteen 

 minutes the water, containing the eggs, is filtered through 

 bolting- silk of 100 meshes per inch, which just allows single 

 eggs to pass through, whilst keeping back clusters of eggs 

 or other large material. The filtrate is divided amongst a 

 number of tall narrow beakers containing sterile sea-water, 

 and the beakers, after being covered with a glass plate, are 

 placed where the temperature will be uniform and not rise 

 much above 15° C. In the course of twenty-four hours the 

 healthy larvae will swim up to the surface and can be easily 

 seen and removed from vessels of this shape. They are 

 transferred by means of sterile pipettes to jars ^ of sterile 

 sea-water, about fifty to seventy larvae being put in each jar 

 of 2000 c.c. sea-water. At the same time, a good pipetteful 

 of a pure culture of diatom is added to each jar. The small 

 diatom Nitzschia closterium, forma minutissima we 

 have found most useful, as its size is suitable, and it grows 

 well in atiimal-charcoal tank-water, floating throughout the 

 body of the water, and so being in intimate admixture with 

 the larviu. The jars are placed in a moderate light and at as 

 even a temperature as possible." No further attention is 

 necessary until the larvae have metamorphosed. The meta- 

 morphosis takes place in from six to nine weeks after 

 fei'tilisation. Larvt« may be taken out from time to time and 

 examined to see if they are feeding well. If the diatoms do 

 not grow sufficiently rapidly in the jar more should be added 

 from the culture flasks. We are more often troubled, however, 

 towards the end of an experiment, by an excessive abundance 

 of diatoms. In this case the jar may either be put in a 

 darker place, or some of the water may be drawn off and 

 replaced by a fresh supply of sterile sea-water. Care should 



' The vessels we use are ordinary gi-een-glass sweet-jars, having a 

 capacity of about 2000 c.c, which are kept covered with the glass stoppers 

 provided with such jars, from which the cork band has been removed. 



- In hot weather we often stand the jars in one of the tanks of circu- 

 lating aquarium water, which maintains them at a veiy uniform tempe- 

 rature. 



