426 E. J. ALLEN AND E. W. NKLSON. 



arise, as the larvae do not feed after liatcliing. It must be 

 noted, however, that these larvae had previously been reared 

 by M tiller and by Del age. 



Summary of Method for Rearing Larvae. — We have 

 found tliat the best results iu rearing marine larvae 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 fertilise 

 the eggs should be used. 



(3) Sterile sea-water, treated iu such a way that diatoms 

 etc., will grow well in it, sliould be used. No frequent change 

 of water is then necessary. 



(4) All dishes, jars, instrujnents, and pipettes, should be 

 carefully sterilised before use. Every possible effort should 

 be made to prevent the introduction into the rearing-jars of 

 any organisms other than the larvae to be reared, and 

 organisms on which they feed. The jars should be covered 

 with loosely fitting glass covers. 



(5) The eggs after fertilisation must be separated from all 

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

 the larvie swim up they should be pipetted off into fresh 

 vessels of treated water, so as to leave behind any unseg- 

 mented eggs, etc. 



(6) The food organisms should be small in size, so that the 

 larva3 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 Nitzschia 

 closterium, forma minutissima.) 



(7) The food should be abundant eai-l}--, so that the larvge 

 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 



