54 BIOLOGICAL LECTURES. 



grafting is possible, I can testify, as a result of a repetition of some of the 

 experiments. See Born's paper in Schlesischen Gesellsch. f. vdterldndische 

 Cultur : Medicinische Section, 1894, pp. 13. Supplementing Born's results 

 are Roux's experiments on cytotropism, or the reciprocal attraction of iso- 

 lated blastomeres of Amphibian eggs (^Archiv f. Entwickelungsniechanik, I, 

 1894) if brought close together, though at first not in actual contact. There 

 is also some evidence of asexual caryotropism as witnessed in the conjugat- 

 ing nuclei of the cells of the intestinal epithelium of land-Isopods (Ryder 

 and Pennington, Anat. Anseige?-, 1894). 



The experiments of O. Schultze (Anat. Anzezger, Erganzungsheft zum 

 Bd. IX, pp. 1 17-132, 1894) by very slowly rotating in a mechanically fixed 

 position the segmenting eggs of Amphibians on a specially constructed 

 chnostat, with the result of disorganizing and killing them, shows that such 

 eggs are not isotropic. His production of double monsters in such ova by 

 disturbing, for a time, their geotropic relations, is also significant, while his 

 conversion of the meroblastic amphibian egg into a holoblastic, evenly seg- 

 menting one by merely rotating it through 1 80° out of its normal geotropic 

 relation, and allowing it to complete its segmentation in an inverted position, 

 proves that the egg can be made structurally homogeneous by mere mechan- 

 ical means, but at the expense of its power to complete its development. 

 This is further proof that the egg is not isotropic in the sense in which that 

 word is used by natural philosophers. 



Since the appearance of the short but important paper by Prof. E. B. 

 Wilson and A. P. Mathews {Jour, of Morphology, vol. X, no. i, 1895), 

 in which they deny the existence of the centrosome, it becomes necessary 

 for me to explain that the word " centrosome " is used in the text in the 

 sense in which they use the expression " attraction spheres." Their discov- 

 ery that the ovocenter, or attraction sphere of the egg, disappears after the 

 expulsion of the two polar cells in echinoderm eggs, to be replaced by the 

 spermcenter, is of the greatest significance, and may explain the reason why 

 parthenogenetic eggs develop, namely, as a consequence of their retention 

 of an ovocenter. The new facts that these two able workers have disclosed 

 are entirely in harmony with a dynamical theory of fertilization and sex (see 

 p. 34, and farther, of the text). 



