ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 173 



the artificially induced phenomena should be regarded as intermediate 

 between indirect and direct nuclear divisions, and whether what have 

 been described as genuine amitoses are not really more like the pseudo- 

 nmitoses seen in the etherised eggs. His suggestion is rather that the 

 influence of the ether is to inhibit the cellular development and to allow 

 more primitive conditions to express themselves, especially the tendency 

 towards forming what might be called a composite nucleus out of several 

 independent parts (Teilkerne) corresponding to the individual chromo- 

 somes. 



Isolation of Blastomeres.* — Prof. R. S. Bergh takes a critical survey 

 of the numerous experiments on the isolation of blastomeres — an experi- 

 mental method which has now, in his opinion, reached the end of its 

 tether. He points out that the controversy over the question whether 

 an isolated blastomere of the two-cell stage yielded a hemi- or a holo- 

 embryo has had the useful result of showing that neither result can be 

 called typical, and that even in the same subject (the frog's egg) either 

 result may occur according to the conditions of experimentation. 



Ovulase.f — J. B. Pieri gives the name " ovulase " to a supposed new 

 soluble ferment obtained by shaking spermatozoa of Echinoids for 

 a quarter of an hour in a glass vessel. Tbe fluid induced segmentation 

 of ova to the morula stage, though no fertilisation by stray spermatozoa 

 could be detected. But as the author recognises, the experiments require 

 to be repeated with more rigorous precautions. 



Bilateral Symmetry of Egg.$ —Dr. 0. Schultze has re-investigated 

 the developing egg of liana fusca, with special reference to the question 

 of the exact period when bilateral symmetry makes its appearance. He 

 finds that, though it remains uncertain whether this symmetry does or 

 ■does not appear before fertilisation, it is certain that it is distinct shortly 

 before the appearance of the first segmentation furrow. The plane of 

 symmetry is the median plane of the frog, and is distinct both in the 

 intact egg and in sections. The point of entrance of the spermatozoon 

 is usually exactly opposite the spot where the blastopore ultimately 

 originates, and the pigment track occupies approximately the plane of 

 symmetry ; but deviations from this norm are not infrequent. There is 

 no evidence that the plane of symmetry is determined by the spermato- 

 zoon in eggs in general. Generally, it may be said that there is no fixed 

 period when bilateral symmetry appears. It may in different forms 

 appear either before fertilisation, just before the beginning of segmenta- 

 tion, during segmentation, or at the time of the appearance of the primi- 

 tive streak. The fact that the fir?t segmentation furrow and the median 

 plane of symmetry sometimes appear at the same time does not justify 

 the view that this constitutes a general developmental law. But it may 

 be said that, at least in numerous cases, the segmentation of the epg in 

 a, bilaterally symmetrical animal does not consist in the division of the 

 egg into an irregularly arranged mass of cells, but in a symmetrical 

 grouping of cells about the median plane of the developing organism. 



* Zool. Centralbl., vii. (1900) pp. 1-14. 



t Arch. Zool. Expe'r., vii. (189!)) Notes et Revue, xxix.-xxx. 



J Arch. Mikr. Anat., lv. (1899) pp. 171-201 (2 pis. and 2 figs.). 



