194 Transactions of the 



it has been further confirmed by Coste * for Gasterosteus and by 

 Carl Vogt for Coregonns palea. Strieker f has made assertions 

 respecting Sal mo f aria, which do not agree with those of Eusconi. 



According to Strieker knobs grow from the blastoderm in an 

 irregular series, which become separated by a constriction from the 

 main body of the blastoderm; from the primary knobs grow up 

 secondary ones, which likewise become separated. 



According to Strieker the segmentation, that is the splitting of 

 the whole blastoderm, is completed in forty-eight hours. Strieker 

 came to these conclusions by studying eggs after hardening them 

 in chromic acid. 



I have studied the segmentation of the blastoderm of four sets 

 of eggs of Salmo fario in the living condition, and I have arrived 

 at conclusions, which are in many respects different fi'om those of 

 Strieker, and which agree as regards the first stages of segmentation 

 with the observations made on other Teleostean fishes. 



A fertilized trout's egg exhibits under the microscope, up to 

 the sixth hour, a rather uniform aspect. The egg appears as a dull 

 globe enveloped in a thick vitelline membrane, and shows irregularly- 

 distributed fat-like globules. 



The earliest time, at which I was able to perceive an indication 

 of the blastoderm, was five hours and forty-five minutes after fecun- 

 dation, when there appeared in one place a small, somewhat more 

 opaque, irregularly-outlined spot, in the circumference of which the 

 fat-globules had accumulated. If the breeding apparatus is kept in 

 a cold place, as is generally done, about the tenth or twelfth hour 

 after fecundation, the blastoderm seen from above, or better in profile, 

 appears as a distinct mound, which lies on a saucer-like depression of 

 the yolk : a space is consequently left between the vitelline mem- 

 brane and the yolk (compare Fig. 7 A). In that part of the yolk 

 which represents the bottom of the saucer-like depression lie accu- 

 mulated the fat-globules. 



As soon as the blastoderm appears as a distinct mound, there 

 are to be seen on it very remarkable changes. If we observe a 

 blastoderm carefully for a considerable time with a No. 4 Hartnack, 

 we find at first that its border does not remain in the same con- 

 dition, but exhibits in different places slight changes. On one 

 place, for instance, where the blastoderm has been sharply outhned, 

 its margin becomes more transparent and slightly projecting, as if 

 the mass of the blastoderm at this point had sent out a flattened 

 prolongation ; after a short time the prolongation is retracted, and 

 the general outline of the blastoderm becomes sliarp as before. The 

 same appearance occurs in difierent places. The prolongations of 

 the blastoderm which appear and disappear are of very different 



* ' Histoire de Developm. d. Corps Org.' 



t ' Sitzungsber. der Wiener K. Akadeuiie der Wissensch.,' Bd. 51. 



