I 56 BERTRAM G. SMITH. 



the fact that the eggs are laid in running water, the protection of 

 such an egg from shocks and jars due to impacts against the 

 rocks is an exceedingly important matter, and we find it accom- 

 plished by an admirable adaptation of the egg envelope. The 

 tough but elastic egg capsule is inflated by osmosis with a liquid 

 in which the egg freely floats. The turgid condition of the en- 

 velope increases its efficiency in protecting the egg. While ordi- 

 narily the egg sinks to the bottom of the surrounding liquid, and 

 rests lightly upon the membrane beneath, there is so little friction 

 between the egg and its envelopes that the latter may be rotated 

 without turning the egg. A similar adaptation exists in the eggs 

 of other amphibians, and in the eggs of teleosts (Reighard, '93); 

 but it is particularly well shown in the egg of Cryptobranclnis. The 

 connecting cord is strong enough to support the weight of half 

 a dozen eggs suspended out of water ; it stretches greatly during 

 the operation, but contracts to its usual length when the eggs are 

 returned to the water. This elasticity of the connecting cord 

 serves to deaden any shock to the eggs due to the tugging of 

 the current or to the chain catching on to rocks while floating 

 down stream. 



The egg envelopes further serve to protect the eggs from 

 little fishes that would otherwise devour them. 



If eggs are left for several days undisturbed in the still water 

 of a basin, some of them adhere to the envelopes beneath, inter- 

 fering with the development. Probably under natural conditions 

 the gentle agitation of the current tends to prevent this, perform- 

 ing for these eggs the same service afforded to the eggs of the 

 hen by the mother when she turns them. 



III. SEGMENTATION. 



The perfect transparency of the gelatinous envelopes of these 

 eggs makes them very favorable material for watching the 

 development of the living egg, since the process may be observed 

 without removing the egg from the capsule. The large size of 

 the eggs and the distinctness of the cleavage lines on their upper 

 hemispheres also make them convenient objects for study. By 

 using a mirror both poles of the egg may be watched at the same 

 time, but observations on the lower hemisphere by this method 



