Experiments on the Early Development of the Amphibian Embryo etc. 629 



of the Newt, Triton cristatus. He finds that the first indications of 

 cilia in both species occur shortly before, or just at the time of the 

 closing of the neural folds. The cilia are developed first upon the 

 lateral expansions of the neural plates, and along* its edges, and 

 produce a current whose direction is from before backwards. Later 

 a similar current is produced by cilia upon the ventral surface. The 

 ciliation spreads rapidly until the whole embryo is covered, but the 

 currents differ much in intensity, and are specially developed in 

 certain regions. 



AssHETON concludes that there can be very little doubt that the 

 purpose of this ciliation is respiratory. Such a conclusion is of 

 special significance when taken in connection with the facts observed 

 in the present experiments. In normal embryos the movement of 

 the cilia produces not only a current in the surrounding medium, 

 but also a horizontal rotary motion of the embryo itself within the 

 inner egg membranes. This motion is increased by both salt and 

 Ringer solutions and becomes so persistent that patient watching 

 fails to catch the embryo at rest long enough to sketch it with a 

 camera lucida. In order to obtain this it must first be killed. The 

 cilia are so strong in some instances as to produce the same motion 

 in embryos lying free upon the bottom of the dish, and these, so far 

 as could be determined, were the ones which lived beyond the closing 

 of the neural folds. Ordinarily, however, the greater amount of 

 friction to be overcome against the bottom of the dish rendered such 

 motion impossible. As can be seen from figs. 15 and 16 the chief 

 areas of ciliation are the head, the neck, and a broad band extend- 

 ing obliquely across the sides of the body. When the embryo is 

 freed from the membranes it's weight causes it to rest upon one 

 side on the bottom of the dish, and consequently the cilia upon that 

 side are rendered practically useless. In it's normal position within 

 the egg membranes the fluid which surrounds it is denser than water, 

 and hence more nearly of the same specific gravity as the embryo 

 itself, and the latter has no difficulty in keeping free from the 

 membrane. Furthermore the jelly in which the eggs are enveloped 

 is comparatively thick and firm during earlier development, but 

 gradually softens, and finally goes to pieces and allows the larvae 

 to escape. There would seem to be established in this way a deli- 

 cate adjustment of osmosis, whereby the larva is carried safely beyond 

 the ciliated period and initiated gradually into the less dense medium. 

 The rotary motion produced by the cilia, therefore, is probably of 



41* 



