786 



SCIENCE 



[N. S. Vol. XXXVIII. No. 987 



transplanted for a time in an artificial nutri- 

 ent medium or even in serum from the animal 

 to be grafted, allowing tlius a preliminary ad- 

 justment to the new environment, but have 

 had no opportunity to give such methods a 

 trial. They are mentioned as possible sug- 

 gestions for some one who may be able to at- 

 tack the problem fully equipped with a knowl- 

 edge of the principles governing immunity 

 and anaphylaxis. 



This investigation has been carried out in 

 the Bussey Institution with assistance from 

 the Carnegie Institution of Washington. 

 W. E. Castle, 

 John C. Phillips 



The Bussey Institution 

 Harvard Univeksitt 



nutrition and sex determination in 

 rotifers 



In an interesting paper in the August, 1913, 

 number of the Journal of Experimental 

 Zoology, Claude W. Mitchell communicates a 

 series of observations and experiments upon 

 the rotifer Asplanchna, from which he draws 

 conclusions at variance with those hitherto 

 advanced by investigators who have worked 

 with Hydatina. His main conclusion, it ap- 

 pears to me, is that " qualitative and quanti- 

 tative changes in nutrition will be found the 

 universal sex-controlling factor in this group " 

 (rotifers). If it be granted that other factors 

 than nutrition also play the same role in sex 

 determination in one rotifer as in another, I 

 think it may be shown that Mitchell's experi- 

 ments are not calculated to prove his conten- 

 tions. 



There is, in the first place, some obscurity 

 in the use of the word " nutrition." By the 

 earlier workers on life cycles in rotifers and 

 daphni^ns, nutrition was measured by the 

 quantity of available food. The rate of repro- 

 duction gave a key to the degree of nutrition, 

 but the rate of reproduction was supposed to 

 be proportional to the amount of available 

 food. It is obvious, however, that nutrition 

 may be measured by the quantity of food that 

 an organism can assimilate, which may be in- 

 dependent of the amount available. In rotifers, 



for example, there are periods in which repro- 

 duction and growth are rapid, alternating with 

 periods in which these processes are slow. 

 Mitchell does the service to emphasize this 

 " physiological rhythm." Rotifers in the period 

 of rapid growth will live well under external 

 food conditions that would reduce rotifers in 

 a period of depression almost to starvation. 



When we say that nutrition determines sex, 

 what meaning do we put upon nutrition ? One 

 might assume that Mitchell regards nutrition 

 and physiological " level," to use another term 

 of his, as synonymous, were it not that in the 

 seventh paragraph of his summary he lists 

 them separately. To quote : 



Maximum male production is determined by 

 three factors, physiological rhythm, high nutri- 

 tion and starvation during the growth period. 



If nutrition means the quantity of food 

 available, the evidence in its favor as a sex 

 determinant is so small as to be negligible. 

 The experiments of Mitchell do not prove its 

 effectiveness in Asplanchna, as I hope to show 

 below, and my own work on Hydatina is not 

 only distinctly against it, but explains away 

 the positive results of Nussbaum. If nutri- 

 tion means the quantity of food that can be 

 assimilated, then high nutrition is probably 

 the result of an antecedent physiological 

 change that is not nutrition at all. Rhythms 

 of reproduction and growth occur in Hydatina, 

 in protozoa, in Cladocera, and perhaps many 

 other animals; but so far as I know, the 

 physiological change preceding a wave of rapid 

 growth has not been discovered. It may be a 

 chromosomal change. If the wave of rapid 

 reproduction is accompanied by a wave of 

 many male producers, it seems to me we are 

 much more justifiable in assuming that both 

 high nutrition and male production are here 

 the result of some other physiological factor, 

 than in holding the male production to be 

 a result of the nutrition. That the evidence 

 of high nutrition comes earlier in a series of 

 generations than does the evidence of male 

 production may be due to the fact, true at 

 least for Hydatina, that sex is determined a 

 generation in advance without any visible sign 

 of such determination. I revert to this point. 



