SEGMENTATION 187 



birds was not made until 1847, by Bergmann, 1 - confirmed 

 independently by Coste' 2 in 1850. By 1848 segmentation 

 had been noted in Hydra and various hydroids, in acalephs, 

 in starfish, polyzoa, nematodes, rotifers, leeches, oligochsetes, 

 polychaetes, in most groups of molluscs and arthropods, and 

 in all the vertebrate classes. 3 



The process was at first held to be merely one of yolk- 

 division, or Dotterfurchung, and its details were by most 

 interpreted in the light of the Schleiden-Schwann theory 

 of cell-formation. 



The first steps towards a truer conception of the process 

 seem to have been taken by Bergmann, who in i84i 4 

 called attention to the presence of nuclei in the segmenta- 

 tion-spheres of the frog's egg, and by Bagge in the same 

 year, who observed that division of the nuclei preceded the 

 multiplication of the segmentation spheres. 5 Reconsidered 

 the nuclei to be anucleate cells, and the same view was 

 taken by Kolliker in 1843.''' Next year, however, in his 

 classical paper on Cephalopod development 7 Kolliker came 

 to the opinion that they were really nuclei. He showed 

 that segmentation was brought about by cell-division, that 

 between " total " and " partial " segmentation there was a 

 difference of degree and not of kind, and that the cells of the 

 body were formed by division of the segmentation spheres. 

 He held, however, that the nuclei multiplied endogenously and 

 not by division. The division of nuclei was observed by 

 Coste in i846. s Leydig in 1848 took the necessary step in 

 advance and maintained that the nuclei as well as the cells 

 increased always by division. He was supported by Remak, 

 who in a paper of i852, 10 and more fully in his monumental 



1 Muller's Archiv, 1847. 



- C.R. Acad. Sci., xxx., p. 638. 



3 See review by Leydig in Isis, 1848, pp. i6[-ig3. 



4 Muller's Archiv, pp. 89-102, 1841. 



' De evolutions Stron^yli auric, ct Ascaridis acum., Erlangen, 

 1841. 



Muller's Archiv, pp. 66-141, 1843. 



7 Entwickelungsgeschichte der Ccphalopoden, Zurich, 1844. 



3 Froriep's Notizen, No. 800, 1846. 



9 his, 1848. 



1(1 Muller's Archiv, p. 47, 1852, also 1854 and 1858. 



