ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
G93 
seem to resemble tlie process of segmentation in the blastoderm of a 
fish-egg. Now, what has been abnormally achieved with E. viridis is 
achieved normally with the segmenting blastoderms of many Vertebrates 
and Invertebrates. In them growth proceeds over the spherical surface 
of the yolk under constraint mainly to two dimensions of space. 
The singular fact that the side where the embryo is formed ulti- 
mately often grows slowest is probably to be explained by the blasto- 
derm being thickest at that point ; it, therefore, intussuscepts material 
more rapidly over a smaller area on its under surface at that region than 
elsewhere. Here constraint to growth is less in the third dimension 
than at other points in the blastoderm, and consequently it spreads 
slowest at the tail end of the embryo, or where it is thickest. This 
condition of inequality of thickness serves to explain the origin of 
concrescence. 
Concrescence in a fish-egg, for example, is an effect of the unequal 
growth in thickness of the blastoderm, and is, consequently, to be re- 
garded as an adaptive effect rather than as a cause. 
Extending his view still further, the author sees in “ heredity ” itself 
only an effect, dominated and directed in its progressive complication 
by the laws of the conservation of energy. What the mechanism of 
heredity is remains to be discovered by an elaborate and connected study 
of the phenomena of organic growth, and the mechanisms and corre- 
lations of the same, and not by the assumption of the existence of 
unknowable as well as undiscoverable gemmules, plastidules, or germ- 
plasms. 
Reproduction of Noctiluca miliaris.* — Prof. C. Isliikawa has made 
a study of the division and spore-formation of N. miliaris . The division 
of the animal is preceded by the loss of the peristome, teeth, and ten- 
tacles, but the mouth and “ Staborgan ” are always present ; the spore- 
forming individuals do not possess the two last-named parts. The 
division of the nucleus is always preceded by the concentration of part 
of the cytoplasm in the form of a spherical or oval granular body ; this is 
the archoplasm or kinetic centre of division. In living animals at this 
stage the nucleus appears more or less homogeneous and transparent, 
but, treated with reagents, the chromosomes come into view distinctly. 
Each of these last consists of a row of disc-shaped microsomes irregularly 
scattered in the nucleoplasm ; in the nucleus of a dividing animal each 
microsome-ring splits into half-rings, while in that of the spore-forming 
animal two successive divisions of a microsome-ring take place. The 
chromosomes collect on that side of the nucleus which is nearest to the 
archoplasm, and spread out towards the other pole ; the archoplasm 
divides, and forms a very large spindle which first lies tangentially to 
the surface of the nucleus ; this division is succeeded by the separation 
of the chromosomes into two groups, each attracted (?) by its respective 
archoplasm. The archoplasmic spindle pushes in the nuclear wall on 
which it lies, and the nucleus assumes in consequence the form of a 
half-ring. The fibres of the spindle are continuous from one pole to 
the other, and, as they lie outside the nuclear wall, they become in no 
way connected with the chromosomes. At this stage, however, another 
* Journ. Coll. Sci. Imp. Univ. Japan, vi. (1894) pp. 297-334 (4 pis.). 
1891 3 B 
