BULLETIN OF THE UNITED STATES FISH COMMISSION. 335 



similarly marked, the dorsal and anal with a dark blotch on each eighth 

 or tenth ray, the pectoral sometimes with one or more brownish bars. 



Not abundant in the Bay of Panama; several specimens were taken, 

 the largest about 10 inches in length. 



Indiana University, December 2, 1881. 



OIV THE IVUCL.EAR Cr-EAVAGE-FIOITRES DEVEIiOPEO DURIIVO THE 

 SE«.nE STATION OF THE OERi^lINAI. DISK OF THE EOO OF THE 

 SAIilMOIV. 



By JOHN A. RYDER. 



The fact that very complex changes are undergone by nuclei during 

 the segmentation of cells has been known for only a comparatively 

 short time, and, we may add, our knowledge has been greatly increased 

 by the recent advances made in the perfection of histological methods. 

 The titles of the j)rincipal memoirs on the subject are given below.* 



From the list of papers, it will be gathered that all are German, and 

 by only a few authors. The lirst of them. Professor Flemming, has de- 

 scribed and figured such remarkable cleavage-figures, which he has 

 claimed to have observed in segmenting cells, that it is not to be won- 

 dered at that some cotemporaries have been inclined to be incredulous. 

 Since I have been enabled, however, to observe some of these phenom- 

 ena for myself, I am quite well convinced that he has given us results, 

 the value of which cannot perhaps just yet be proi^erly estimated. 



I recently received a series of ova of the common salmon, some of 

 them in the second day of development, from Mr. H. H. Buck, of Or- 

 land. Me., in which very comi)lex and interesting nuclear changes were 

 in progress. The germinal disk had not yet begun to spread to form 

 the blastoderm, but the cleavage had advanced so far that it had been 

 segmented into several thousand cells, each measuring about 3-5-0 tli of 

 an inch in diameter. These salmon ova had been i)reserved in weak 

 alcohol, so that they were not quite as good, perhaps, for our studies as 

 they would have been had they been hardened in very weak chromic 

 acid. The cells were, however, very clear, so that any nuclear figures 

 could be well seen even without other reagents, though upon immers- 



*^W. Flemming. Beitrjige ziir Kentniss der Zelle unci ihrer Lebenserscheiniiugen. 

 I Part, Arch. f. mikr. Anatomie, XVI; II Fart and supplement, Ibidem, XVIII; III 

 Part, Ibidem, XX. 



W. 'Flennning. Ueber das Verhalten des Kerns bei der Zelltheilung und Uber die 

 Bedentimg mebrkerniger Zelleu. Virchow's Archiv, LXXVII. 



Peremescbko. Ueber die Theilung tbierischer Zellen. Arch, f. mikr. Anatomie, 

 XVII. 



W. Pfitzner. Die Epidermis der Ami^hibien Morphol. Jabrb., VI. 



W. Pfitzner. Ueber den feinereu Ban der bei der Zelltheilung auftretenden faden- 

 formigeu Differencirungen des Zellkerns. Morph. Jahrb., VII, lift. 2. 



W. Pfitznex-. Beobacbtungen iiber weiteres Vorkommen der Karyokinese. Arch. 

 f. mikr. Anatomie, XX, Hft. 1. 



