BY R. J. TILLYARD. 397 



means of gauging the extent of the change. But for this, T 

 doubt if I should have noticed the gradual beginning of the 

 change at all. 



The behaviour of the second pronymph was not exactly tlie 

 same as that of the first. After remaining weak and inert for 

 about two hours (by which time the first pronymph had been 

 just disposed of), I found that it had become much more vigorous, 

 making many attempts to burst the pronymphal sheath, all of 

 which, unfortunately, were failures. A count of the pulse, during 

 tlie most active of these attempts, showed 70 beats to the minute. 

 A few minutes later, I took a fine brush, and coaxed the pi"o- 

 nymph out from its egg-shell. It at once began to bend up 'and 

 down vigorously, and made frantic ett'orts to break its sheath. 

 Soon after, I noticed the pulse quicken greatly, and a count gave 

 120 beats to the minute. On searching for the cause of this, I 

 found that the sheath liad l)iu'st dorsally over the sixth abdominal 

 segment, and that the hir\ul intestine was pi-ojecting through the 

 slit. This, of course, meant a speedy death to the larva. This 

 second pronymph, therefore, lived just over two hours, and no 

 gas appeared in its tracheal system during that period. 



Watch was continued throughout April 3i-d. On that day, 

 two more pronymphs emerged, both, unfortunately, after dark, 

 and at a time when I was only able to pay occasional visits to 

 the microscope. Complete] v tired out with the four days' 

 watching, I \\as in no mood to continue the watch far into the 

 night, and contented mj'self with noting that the general course 

 of events, in the cases of these two, was \ery similar to that in 

 the first pron3"mph. The tracheal system showed no signs of gas 

 until about three hours after hatching; and the gas, when present, 

 did not extend beyond the limits stated in the first case. Both 

 these nymphs were found dead in the morning, having failed to 

 burst their sheaths. 



Before describing the remaining experiments made upon these 

 eggs, it would be best to give in tabular form the full record of 

 emergences for the Series A, B, and C, in order that references 

 to the table may make these experiments clearer. 



