386 T. H. MORGAN AND UME TSUDA. 



to the egg is shown in PI. 25, fig. 5. In some cases the 

 embryo measures a little more than one third of the periphery, 

 in others a little less. Very quickly after the appearance of 

 the medullary folds the embryo increases in length, and the 

 proportions of the egg change, so that in order to determine 

 accurately the length of the medullary folds as compared with 

 the egg they must be measured when their outlines are just 

 indicated by darker pigment. 



The suckers appear in front of the medullary folds, and 

 arise at about the same time : a dark line of pigment marks 

 their position. This crescentic line of pigment — the beginning 

 of the suckers — is not quite halfway around the egg from the 

 blastopore, i. e. it is nearer to the dorsal lip of the blastopore 

 than to the ventral. 



Experimental Investigation. — Loss of time and ma- 

 terial was caused at first by attempts to do experiments that 

 proved to be impossible ; also many results were valueless, 

 because the eggs experimented upon were not watched con- 

 tinuously. I cannot too strongly emphasise this point, that 

 unless each egg is carefully followed, from the moment of 

 injury to the time of preservation, the results become uncertain 

 and of little value. I have seen an injured point completely 

 heal over, and the extra-ovate of Roux plough a long furrow 

 over the surface of the developing egg; consequently any 

 conclusion drawn from the end result without a knowledge 

 of the intermediate stages would lead to error, and I cannot 

 but think that some of Roux's earlier experiments that seem 

 to be so contradictory may have been caused by some such 

 changes. 



Futile attempts were made to remove as much as half the 

 yolk and protoplasm from the fertilised egg. Such eggs col- 

 lapsed completely. Equally unsuccessful were attempts to 

 add the yolk removed, by means of a hypodermic syringe, to 

 another egg. 



At the two-celled stage, just as the four-celled stage was 

 beginning, attempts were made to suck out with a syringe all 

 of the protoplasm from one hemisphere, in order to determine 



