APPENDIX 2 215 



Variance. A measure of the variability in a series of numbers. The mean of 



the squares of the deviations from the mean. 

 Velum. Fold of tissue at the posterior part of the pharynx of a tadpole. 

 ViTELLUS. That part of the egg that develops into the embryo. The black 



centre of the egg. 



