442 MORRIS M. WELLS. 



flowing. No attempt was made to remove the plankton from 

 this water and if the starving animals secured food from it the 

 amount was far from sufficient to meet their normal needs, for 

 the loss of weight due to starvation proceeded uniformly with 

 the exception of two weighings (see Table I.) up to the death 

 point. The aquaria were kept free of plant growth and no food 

 of any kind was given the animals. 



After the initial weighing the starving fishes were reweighed 

 at gradually increasing intervals. Thus at first they were 

 weighed every other day while later a week or ten days was 

 allowed to elapse between weighings. 



It was noted that the weight of the fishes varied slightly with 

 the temperature of the water in w r hich they were confined just 

 previous to being weighed. A fish which weighed 32 grams at 

 5 C. weighed 32.1 grams after being placed in 12 water for 

 15 min. Another fish weighed 71.8 grams at 5 and 72.1 grams 

 at the end of 15 min. in 12 water. This temperature factor 

 was eliminated by weighing the fishes rapidly when they were 

 taken from the aquaria for the temperature of the aquarium 

 water changed but slightly after December I (varied between 

 4 and 8 C.). 



The rock bass was selected for the experiments herein recorded 

 because this species at the time, was easily caught by seining, 

 in the small streams in the Chicago region; and it had been 

 noted during several years of collecting that the individual fishes 

 seemed to fall into natural size groups which were apparently 

 correlated with age. Five of these groups are readily distinguish- 

 able and a sixth is sometimes taken. 



The smallest fishes collected weighed from 1-1.5 grams and 

 were evidently the fry of the previous spring. The next larger 

 group averaged from 10-15 grams and included fishes that were 

 probably a little over a year old. The third group weighed 

 from 25-40 grams, the fourth from 80-100 grams and the fifth 

 from 100-125. It is at least possible that these latter groups 

 are made up of fishes that are in their third, fourth and fifth 

 years respectively. Occasionally still larger individuals weighing 

 over 130 grams were taken. Not enough of this group was taken 

 to include it in every experiment and it is probable that fishes 



