Object mid Fimction of the Egg-stalk. 125 



Fig. 8) contains an embryo in which the rudiments of 

 the head and mouth are all that can yet be distinguished 

 with certainty; but even at that early period, regular 

 rotation takes place, by which we sometimes obtain 

 a side view, and sometimes a front view of the embryo. 

 These movements follow with a slow, wave-like succession 

 peculiar to sarcode, and are unlike the quick contractions 

 of true muscular tissue. It is possible to observe this 

 embryonic state six weeks before the larva attains per- 

 fection. Where such continuous movements are taking 

 place, a supply of oxygen appears to be indispensable. 

 The egg, however, while lying deeply in the heart of the 

 bud, can only obtain this supply of oxygen through the 

 egg-stalk, because no gaseous interchange can take place 

 through the thick walls of the bud. The surrounding 

 plant tissue which is in a state of rest, and in which no 

 metabolism is going on, can afford no such supply. 

 This, it will be seen, imparts a fresh importance to the 

 fact that the egg-stalks are of varying length. If the 

 egg-stalk had only been intended for the purpose of 

 dragging the e:gg along the ovipositor when it was 

 being laid, a short egg-stalk would have been sufficient. 

 But the lengths are very different, and I believe I can 

 show that they are regulated by the thickness of the 

 layer that separates the egg-bodies from the surrounding 

 atmosphere. As the egg-stalk is a continuation of the 

 yolk sac, and ought to remain in the closest possible 

 relationship with the air, we find that a long stalk is 

 constantly present in eggs which are deeply sunk in the 

 bud. As a rule, a long egg-stalk belongs to a long 

 ovipositor, but there are exceptions, and it is precisely 



