No. 2.] FORMATION OF THE FISH EMBRYO. 455 



fischembryo steht, wie man sieht, durchaus in Uebereinstim- 

 mung mit den Folgerungen, die aus meinen Versuchen am 

 Froschei sich ergeben haben. ... Wir konnen daher den 

 Satz aufstellen: Die schwarze am Eiaquator angelegte Ur- 

 mundslippe des Froscheies entspricht dem Randwulste der 

 Knochenfische. Das Material fur die Medullarplatte des 

 Froscheies liegt in und wohl noch neben dem ganzen, das Ei 

 rings umziehenden Umschlagsrande des Epiblast in den 

 Hypoblast." 



Further, Roux has recorded cases of abnormal embryos, m 

 which the medullary plate appears as a ring encircling the 

 equator of the egg. 



I have been able to produce the latter kinds of embryos arti- 

 ficially (10) by the addition of a definite amount of salt to the 

 water during development. From a study of a number of such 

 embryos I have tried to show that we cannot conclude, from 

 what happens in such cases, what the normal processes really 

 are. My reason for this statement was that in many such 

 embryos the open ring may include a length far greater than 

 the length of the normal medullary plate. 



Later (9) I suggested that, in such cases, the medullary 

 plate at the dorsal lip was prevented from growing along its 

 meridian, and therefore, its substance had divided into two 

 portions which migrated around the egg equator, to form the 

 medullary plate and notochord. This is the same suggestion 

 which Oellacher advanced to account for similar embryos of 

 Teleosts, modified in the same way as the frog. 



In regard to Roux's experiments, where definite points of 

 the egg were injured, I admitted that, if verified, they gave 

 strong evidence for Roux's conclusion. 



During the present spring, 1894, I have made a very large 

 number of experiments on frogs' eggs, and have reached 

 the conclusion that Roux's position was well taken. I have 

 found that injuries made laterally, just outside of the black- 

 white line, do pass up into the medullary plate, and ultimately 

 may reach nearly the middle line of the embryo. 



I have, further, made many experiments by destroying the 

 dorsal lip of the blastopore. From these we see that even 



