ON THE ARTIFICIAL CULTURE OF MARINE PLANKTON ORGANISMS. 471 



their liost, Carcinus mnenas. These larvie were kept in aquarium 

 tank-water treated with animal charcoal and filtered through a 

 Berkefeld filter. In this case the question of food did not arise, as 

 the larvre do not feed after hatching. It must be noted, however, 

 that these larvae had previously been reared by Miiller and by Delage. 



ISummary of Method for Rearing Larva'. We have found that the 

 best results in rearing marine larvte have been attained by taking the 

 following precautions : — 



1. The eggs of the female selected must be really ripe, and the 



spermatozoa of the male active. 



2. The smallest quantity of sperm necessary to fertilize the eggs 



should be used. 



3. Sterile sea-water, treated in such a way that diatoms, etc., will 



grow well in it, should be used. No frequent change of water 

 is then necessary. 



4. All dishes, jars, instruments, and pipettes should be carefully 



sterilized before use. Every possible effort should be made to 

 prevent the introduction into the rearing-jars of any organisms 

 other than the larvie to be reared, and organisms on which they 

 feed. The jars should be covered with loosely fitting glass 

 covers. 



5. The eggs after fertilization must be separated from all 



foreign matter, pieces of ovary, or testis, etc. As soon as the 

 IsiYvx swim up they should be pipetted off into fresh vessels of 

 treated water, so as to leave behind any unsegmented eggs, etc. 



6. The food organisms should be small in size, so that the larvas 



can draw them into the mouth by ciliary currents. The food 

 should distribute itself through the body of the liquid and not 

 settle too readily on the bottom of the vessel. (This is one of 

 the great advantages of the diatom Nitzscliia clostcrium, forma 

 minutissima.) 



7. The food should be abundant early, so that the larvie may 



commence feeding as soon as they are able to do so. The food, 

 however, must not be allowed to get excessively thick in the 

 water. It can be kept down by diminishing the light .or by 

 changing some of the water. 



8. The temperature should be kept as constant as possible. Within 



limits, the actual degree of temperature is not so important as 

 the avoidance of rapid change of temperature. 



9. A good north light, not exposed to direct sunlight, is most suit- 



able for the rearing-jars. 



NEW .SERif;s.— VOL. VIII. NO. 5. Mauch, 1910. 2 K 



