BV R. .t. tlLLVARt). 409 



eggs hatched, and yielded liealthy larvse. We miifst coneliide, 

 therefore, that the restriction of the amount of water allowed to 

 Series B, and the covering-over of the crystal dish (except on 

 rare occasions for a few nioments) by a glass slide, to prevent 

 free aeration of the water, liad no appreciable effect upon the 

 course of development. 



The only difference between Series A and Series B was the 

 /■'')Nt)nf/ of the vPAjetahle tissues from around the eggs of the former 

 series. The results, as we have seen, were disastrous. Sixteen 

 embryos died, six reached the pronymphal stage, and six just 

 got as far as the larval stage, but were too weak to go on living. 

 We can only conclude that ilv vexjetahle tissues play an important 

 jxirf in the oxyyenation of the embryo. 



Let us nt)w consider the peculiar case of the pronymph in 

 Series A, which emerged on April 7th (marked IP* in the Table). 

 .Vs ahead V stated, this was the only embiyo in Series A, which, 

 when iirst subjected tti the conditions of the experiment, had not 

 undergone the process of reversion. The fact that it was already 

 behind the rest of the eggs 'u\ development might suggest some 

 inherent weakness in this particular individual; but there is no 

 i-eason to suppose that it would not have gone on developing 

 normally, if left to itself. That it was not parasitised is clear 

 from the fact that it finally hatched out. Also, since the eggs 

 were all laid together in a regular spiral, on the single piece of 

 stem, we have no reason to believe that it was not one of the 

 same batch of eggs as all the rest. The fact that, in Series C 

 under normal conditions, the eggs continued to hatch over a 

 period of nine days, shows us that considerable variations in the 

 length of embryonic existence are to be expected. This egg 

 merely happened to be tlie most backward of the whole set. The 

 effect of the new conditions upon it was most marked, because it 

 had developed less far under normal conditions. It was, however, 

 a very unexpected and extraordinary thing, to my minfl, that 

 the process of reversion, which should have normallv followed in 

 this case within a dav or two, should Ix' completely pri'vented, 

 and that the embryo should go i>n developing, as it did, liead 



