SPACE FACTOR AND GROWTH RATE li^7 



2. The depth of the culture medium (Spring Water or Standard Solution) must 'be main- 

 tained constant- If there ia evaporation this loss should be replaced with glass 

 distilled water. The water need not be changed until the tadpoles hatch, unless 

 it becomes turbid. If the aquarium is covered with a glass plate and is placed 

 in uniform light and heat, it will require no care until after the beginning of 

 feeding. (Eemove all dead eggs and embiyos, recording the fact,) 



5. After the absorption of the external gills, begin to feed the tadpoles on the 

 standard diet of washed and softened spinach. The green leaves should be washed 

 in running water, and softened by par-boiling. Tadpoles must be cleaned and fed 

 daily thereafter. On occasion it may be necessary to remove all tadpoles to 

 marked crystallizing dishes for a few minutes while giving the aquarium a 

 thorough cleaning, to avoid bacterial contamination. 



OBSERVATIONS AM) EXPEBIMEMTAL DATA: 



In the beginning the record will consist merely of staging the embryos under the 

 various space conditions. After the tadpoles hatch, it will become necessary to make 

 three records from each of the groups of tadpoles at each reading. It is suggested that 

 the readings be taken at weekly intervals. The three records will be (a) size of the 

 largest tadpole (b) size of the smallest tadpole (c) average of five sizes. Such size 

 readings can be made quickly in Petri dishes over scaled graph paper, and are total 

 length. After about 2^ months (at ordinary laboratory temperatures and adequate feeding) 

 the forelimb emergence will be detected in some specimens. This may be taken as the final 

 step in the experiment, i.e., when ^0% of the tadpoles reach forelimb emergence. Eecord 

 the data in the following manner: (See record on following page. ) 



DISCUSSION: 



During the early cleavage stages there may be no detectable difference in the rate of 

 development under the various conditions of reduced crowding. As soon as there is freedom 

 of movement the tadpoles must seek out their food and, in doing so, encounter each other 

 and they are thereby stimulated to further activity, and we begin to find differences in 

 growth rate. Even in the same clutch of eggs there may be genetic differences which might 

 explain differences in growth rate, hence it is Important to compare the averages and the 

 composite averages from the compartments of the same number. The groups are so 

 arranged to minimize any differences relative to the accumulation of metabolites and 

 faecal waste. The single variable in this experiment is supposed to be the available 

 space per tadpole, all other factors of oxygen, food, light, temperature, etc. being equal 

 for all specimens. The surface area is identical for all compartments, and presumably the 

 dissolved oxygen is the same, particularly if the activity of the tadpoles causes suffici- 

 ent agitation of the medium to circulate all dissolved gases to an homogeneous condition. 

 Lynn and Edelman (I956) have carried this experiment to metamorphosis and find that crowd- 

 ing not only affects the rate of development but the success of achieving metamorphosis. 

 The optimum conditions for development, at least in the pre-feeding stages, is a ratio of 

 1 tadpole per 2 cc. of medium in a total of 50 cc. per finger bowl. After feeding begins, 

 this ratio would be considered as definitely crowding the tadpoles and development woilld 

 be consequently retarded. 



