ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
407 
places, and actually lead to the new formation of more than one lens. 
Regeneration is effected by the upper portion of the iris, never by the 
lower. The process may occur in complete darkness, but it is then 
slower than in the light. Any tearing or dislocation of the iris may 
serve as the stimulus to lens-regeneration. 
Neurenteric Canal.* * * § — Herr Kopsch maintains that in Tunicates the 
blastopore becomes the neurenteric canal through the appearance of 
the medullary canal, and that the region of the neurenteric canal is to 
be regarded as a growth-centre from which the elongation of the em- 
bryonic body proceeds. 
b. Histology. 
Present Position of Some Cell Problems.f — Prof. J. B. Farmer takes 
a survey of some recent work, discussing the conception of the cell as a 
structural unit or unit-protoplasmic area, the intercellular continuity of 
protoplasm, the interrelations of nucleus and cytoplasm, the role of the 
centrosome, the phenomena of nuclear division, the problem of reducing 
divisions, and so on. The essay may be recommended as a readable and 
up-to-date statement of the present position of some of the fundamental 
problems of cytology. 
Indirect Division.^ — M. Joannes Chatin has studied direct or 
amitotic division, especially in Paludina affected with cercarise. The 
rapid proliferation in the connective tissue is very instructive ; some 
interesting cases of anomalous direct division occur. Chatin refuses 
to admit the generalisation that indirect division is regenerative, and 
direct division degenerative. Except in special cases, there is no anti- 
thesis between the two modes. 
Annular Nuclei.§ — Prof. E. Ballowitz discusses the annular and 
perforate nuclei which have been described in many different kinds of 
cell. The facts point to the conclusion that these forms are normal 
and potent, and without evidence of degeneration. Moreover, they 
multiply, like other nuclei, by mitosis. Ballowitz has studied them 
especially in the epithelium of Salpci. 
Superficial Position of Central Corpuscles in Epithelial Cells. |] — 
Prof. E. Ballowitz brings together a number of cases, observed by himself 
and others, in which the centrosomes of epithelial cells lay superficially. 
The hypothesis is suggested that the centrosomes may be peculiarly 
receptive to external stimuli, and may transmit these to the general 
protoplasm. In other words, the centrosomes may represent “ a kind of 
sensory, central, primitive organ of the cell.” This seems going even 
further than von Lenhossek’s description of the little body as a “ kinetic 
central organ.” 
Intermediate Body in Cell-Division, f — Prof. E. Ballowitz gives a 
critical account of what is known in regard to this little body. Like 
Flemming, he finds the earliest hints of it in connection with the con- 
necting threads ( Verbindungsfaser ) between the daughter-nuclei. It 
* SB. Ges. Nat. Freunde Berlin, 1897, pp. 5-13 (3 figs.). 
t Nature, lviii. (1898) pp. 63-7 (11 figs.). 
X Comptes Bendus, cxxvi. (1898) pp. 1163-6. 
§ Biol. Centralbl., xviii. (1898) pp. 286-99. 
II Anat. Anzeig., xiv. (1898) pp. 369-72. ^ Tom. cit., pp. 390-405. 
