390 EMERGEXCE OF DRAGONFLY-LAEV.E, 



minute or a little longer. During most of this time, convulsive 

 struggles on the part of the emerging larva make direct observa- 

 tions very ditiicult. I was unable to see the actual beginning of 

 the entry of the gas into the tracheal system of the larva. In 

 the pronymph, the whole tracheal system is filled with a pale 

 yellowish liquid, indistinguishable from the blood in the general 

 body-cavity or ha^mocnele, except that it contains no corpuscles. 

 When, after a short but active struggle, the young larva is free 

 from the prouymphal sheath, gas can be seen travelling down the 

 main tracheal trunks from the anterior mid-gut region backwards. 

 I was able to watch this gas gradually occupy the rectal i-egion, 

 where every tiny capillary in the gill-basket can be seen becoming 

 filled with gas, in a very regular and beautiful manner. 



Now we cannot be content with the imperfect observation 

 that the gas comes into, the tracheip at some level anterior to the 

 rectum. That is, indeed, an important point, since it removes 

 the initial difficulty of understanding how rectal respiration could 

 be carried on by diffusion of oxygen into the rectal capillaries, 

 from the circum-ambient water. But it is not enough. What 

 we need to find out, and what is precisely the most difficult fact 

 to discover, owing to the rapid nature of the emei'gence, is 

 exactly where, when, and how the first gas enters the tracheal 

 system. The following method of solving the problem suggested 

 itself to me, and proved more successful than I had dared to hope. 



It is a well-known fact that dragontly-eggs are always laid so 

 as to avoid direct contact with the aii', even for a few seconds. 

 Such contact seems to be fatal, probably owing to the dessicating 

 influence of air upon eggs constructed especially for submergence 

 under water, or for existence in other moist conditions. In the 

 case of pxcrphytic eggs, i.e., those laid outside the tissues of plants, 

 a gelatinous envelope protects them from the air during the short 

 time that elapses between their passage from the body of the 

 female and their being dropped into water. In the case of 

 endophytic eggs, i.p., those laid Inside the tissues of plants, the 

 female bores with her ovipositor well into the cambium of the 

 plant, and deposits her eggs in the moist tissues. 



