1ST CLEAVAGE FURROW. 



■PER BLAST 





Fig 1^9. Early development of the sea bass, Serraniis atrarius, and the trout, Salmo 

 fario. (A-M after Wilson, 1889 and 1891; N-R after Kopsch, '11.) (A) Two-blastomere 

 stage, showing anaphase of next division. (B) Eight-blastomere stage (slightly modi- 

 fied). (C) Sixteen-cell blastoderm. (D) Sixteen-cell stage, showing anaphase nuclei 

 of next division. In the four centrally placed cells, the spindles are at right angles to the 

 surface, thus forming a latitudinal cleavage furrow in these cells. (E) Section through 

 center of four-blastomore stage. (F) Section through center of (D). Observe periblast 

 tissue. (G) Section showing change from 16-cell stage into 32 cells; see (D). (H) 

 Thirty-two to 64 cells. (1) Late cleavage blastoderm. Observe marginal and central 

 periblast. (J) Multiplication of periblast nuclei around the margin of the blastoderm. 

 (K-M) Late blastoderm, showing marginal and central periblast tissue. (N-R) Cleav- 

 age of the blastodisc of the trout. Observe that periblast tissue is derived from the 

 blastodisc cytoplasm directly. 



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