210 Phylum Art hr op o da 



ploy approximately the minimum dilutions suggested above and grad- 

 ually increase the strength of the medium. Medium that is unnecessarily 

 weak will give rise to small clutches of young — fewer than 8 per first 

 clutch for Daphnia or Simocephalus or fewer than 12 for Moina. First 

 clutches of 10 to 18 Daphnia or Simocephalus or of 15 to 25 for Moina 

 are to be expected under approximately optimal cultural conditions. 

 Over-dilution is also indicated by too little apparent density of the 

 medium. In 200 cc. large-mouthed, tall salts bottles it should be 

 moderately opaque grayish brown when first placed in the bottles and 

 be fairly clear of suspended matter and of a light amber color after two 

 days in the bottles. Over-strong medium is indicated if it appears too 

 dense or (other conditions being normal) if a considerable percentage of 

 newly transferred animals die, if the development is retarded and clutches 

 of young are small and are produced irregularly, if embryos die in the 

 mother's brood chamber, or (Moina) if first clutches are large but many 

 of the mothers die after their young are released. A little experience will 

 dictate the amount of dilution to be employed. Two successive make-ups 

 may require somewhat different dilutions. The worker must decide by 

 inspection when the dilution is sufficient. 



In the writer's laboratory this medium has proven eminently satis- 

 factory when made up with pond water and with horse manure in the 

 proper condition; when the medium has been used with some of the silt; 

 and when it is properly diluted, over-strong medium being especially 

 avoided. This medium has been used by us primarily for rearing to ma- 

 turity or longer, without change of medium, cladocerans in 200 cc. bottles 

 (half filled) in pedigree cultures of several species and many different 

 clones of Cladocera. Excellent reproducing specimens for laboratory 

 use may be reared from young in 6 to 8 days with 2 to 4 per bottle. 



Dr. D. D. Whitney has used a similar stable tea medium for rearing 

 Hydatina asplanchna and other rotifers. In all probability this medium 

 may prove useful for other aquatics {e.g., mosquito larvae, etc.) which 

 may be fed primarily upon bacteria and which flourish in natural waters 

 containing considerable organic matter. 



Bibliography 

 Chipman, W. A., Jr. 1934. A new culture method for Cladocerans. Science 



79:59- 

 Stuart, C. A., McPherson, Maurita, and Cooper, H. J. 193 1. Studies on bac- 

 teriologically sterile Moina macrocopa and their food requirements. Physiol. 

 Zool. 4:87. 



