102 J. Thos. Patterson. 



Abnormal yolk or periblastic nuclei arc found in many meroblastic 

 eggs, especially those of the fish. Several of the nuclei figured by 

 Raifsele, '98, for Belone, greatly resemble what I have observed in 

 the Pigeon, and in the eggs of Squalus also are found many such 

 nuclei. So far as I am aware, no one has described the complete 

 fragmentation of the periblastic nuclei in the bird's egg, although 

 Harper, '04, observed abnormal ones in early stages of the pigeon's 

 egg. He regarded these as spei*m nuclei, but in the light of Miss 

 Blount's, '07, work, they are doubtless to be considered as periblastic 

 nuclei, and are therefore undergoing this disintegrating process. 



Fig. XIV. A is from the blastoderm shown iu Fig. XII. It shows the 

 chromatin lying free in a finely grannlar area among the yolk spherules — 

 the nuclear membrane having disappeared. B is a yolk mass in which are 

 two fragmenting nuclei. This mass had arisen from the yolk lying beneath 

 the archenteron, and doubtless had taken up two degenerating nuclei which 

 were in the central periblast. X 250.. 



The position of these nuclei within the egg is of importance ; for 

 in the main they are located in the region where the zone of junction 

 is being interrupted. In the blastoderms illustrated in Figs. VI and 

 VII they are found mainly in the yolk lying beneath the posterior 

 margin — the rest of the edge being almost wholly free from them, 

 in some cases entirely so. Later, when invagination begins, they 

 are found around the greater portion of the margin (e. g., in the series 

 shown in Fig. VIII), and still later, they may be seen in all parts 

 of the edge, but not in such abundance in the anterior half of the 

 blastoderm as in the posterior, except during late gastrulation, when 

 practically all of the nuclei beneath the archenteron have completely 

 disappeared. In some few cases, however, even in late gastrulation. 



