W. E. Agar 311 



as nearly as possible at the same stage of the life cycle. The successive 

 adult stages of the female are conveniently marked off by the laying of 

 a batch of eggs immediately after each ecdysis. In the male there are 

 no such prominent landmarks, and in order to insure that all specimens 

 measured should be as nearly as possible at the same stage of growth, 

 the males were measured when 20 — 21 days old — that is to say, about 

 twelve days after attaining sexual maturity. Even at this age, however, 

 there is a good deal of variation in body length caused by environmental 

 influence, and as on the whole large males have relatively even larger 



abdominal processes, the ^ ratio in the male is subject to the disturbing 



effects of environment as in the female. Fortunately, the difference 

 between the male ratios in the parent species is so much greater than 

 the modification caused by environment that the latter do not cause 

 any serious inconvenience. 



In order to make the measurements, the animals were anaesthetised 

 by placing for a minute or two in 1 °/^ ether solution \ They were then 

 placed on a slide and measured with an eye-piece micrometer under a 

 combination of lenses which would give a measurement extending over 

 as long a stretch of the scale as possible. The values of the units of 



1 This causes no ill effects. The animals may be kept completely anaesthetised in this 

 strength of ether for several hours, and recover perfectly on return to pure water. 



