13. THE SPACE FACTOR AND THE RATE 

 OF GROWTH AND DIFFERENTIATION 



PURPOSE: To determine the relation of the single factor of space (lebensraum) to the 

 rate of growth and differentiation of the tadpole. 



MATERIALS: 

 Biological: 



Technical: 



Ovulating female, and males of Rana pipiens (or any Anuran). 



Slate bottom aquaria measuring 12 x 24 x 4 inches, sub-divided by fine- 

 meshed wire (galvanized) screen into 6 compartments measuring 8x6 

 X 4 inches. The screen may be held in place by paraffin, permoplast, 

 or slit rubber tubing. The purpose is to provide free circulation of 

 food, respiratory gases, and waste matter throughout the entire aquar- 

 ium. The medium and all faecal material must be drained off by 

 siphoning at increasingly frequent intervals as development progresses. 

 (Other types of aquaria, such as enamel pans, can be adapted to this 

 experiment. ) 



METHOD: 



Precautions : 



1. Make the compartments escape-tight, so that swimming tadpoles cannot 

 move from one compartment to another. Wire mesh must have smaller 

 holes than the diameter of the eggs used. 



2. With some crowding, it will become increasingly important to change the 

 medium frequently. A gauze-covered siphon tube may be used to remove 

 the water, but when the faecal matter is abundant, it may be necessary to 

 remove the tadpoles from a compartment and use the uncovered siphon. Re- 

 move dead animals immediately. 



Control : The variations in numbers in the different compartments will include what 

 may be considered the control, i. e. , that compartment in which there is max- 

 imum or most rapid growth. 



P r o c e du r e : 



1. Ovulate the female in the usual manner, fertilize the eggs and allow them to 

 cleave. At the 2-cell stage remove eggs from the cluster and place them in 

 groups of no more than 5 in each of the compartments, the total number per 

 compartment being indicated in the diagram below. 



<- 



-21*"- 



12" 



^wlre screen 



U" deep 



♦ Number of animals per compartment 



149 



