484 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [30] 



a great nnmber of segmentation spheres, comprising the segmented germ- 

 disk or arcliiblast, and tlie multinucleated parablast. From the archi- 

 blast all of the germinal layers are developed; never does the parablast 

 take part in their formation. That this is the fact is best shown by 

 means of sections, prepared from embryos in much more advanced stages 

 of development, in which the intestine has been developed, and in which 

 we still find these same free nuclei as at first. Wc may then rightly 

 inquire what is the significance of the protoplasmic covering of the food 

 yelk in which a great multitude of free nuclei are imbedded. The only 

 answer which I can give to this question is the following: The para- 

 blast, so rich in free nuclei, assimilates the constituents of the food-yelk, 

 in order to convert them into a form suitable for the growth of the cells 

 of the archiblast, or to convert the yelk into the embryonic layers de- 

 veloped from the archiblast; in other words, the multinucleated para- 

 blast assumes the role of provisional blood. This view I would justify 

 by the three following sets of facts: (I.) The germ-disk already begins 

 to grow during segmentation. This growth can only take place by the 

 incori)oration of nutritive material which can only be supplied by the 

 food-yelk. (2.) During the later stages of development, underneath 

 the embryonic layers, that is, under the embryo itself, one finds the 

 free nuclei heaped upon each other in several layers, and the protoplas- 

 mic layer in which they are imbedded very strongly developed, while 

 around the other parts of the yelk they are sparingly developed. (3.) 

 If one places the eggs under conditions injurious to their development, 

 allows them to remain, for example, in stagnant instead of running 

 water, they become abnormally affected. If such eggs are more closely 

 investigated, it is learned that it is the free nuclei which are first af- 

 fected, in that a fatty degeneration occurs in them, and as soon as ab- 

 normal changes occur in the free nuclei, one may be certain that in a 

 short time the germ, or embryo, will be found dead. The free nuclei are 

 also of great importance in nourishing the germ; that is, the embryo. 



"What is the fate of the free nuclei, whether the3" have only a tran- 

 sient existence, or whether the protoplasm in which they are imbedded 

 divides into definite tracts, or, in other words, whether the free nuclei 

 become differentiated into cells at a later period, I do not know, as my 

 investigations have not proceeded so far. If the view should be confirmed 

 which has been taken of them by His — who at any rate erroneously re- 

 gards these nuclei as originating from leucocytes, which have entered 

 the immature egg — that they become blood corpuscles later, an opinion 

 with which Balfour concurs in regard to their fate in the ova of cartilagi- 

 nous fishes, would be the strongest evidence in favor of my own view, that 

 they functionate as provisional blood during development. It would 

 then throw light, in a remarkable way, upon the genesis of the blood, 

 as the first blood corpuscle would then be formed at the moment when 

 the egg was divided into the archiblast and parablast or into germ and 

 food-yelk. Kupffer's statement that in just hatched embryos of the her- 



