ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
21 
Cryptogams are attracted, as Pfeffer and Dewitz have shown, to certain 
fluids. There is certainly an attraction towards substances and towards 
surfaces, but the fundamental force is an attraction of masses. What is 
true of the heavenly bodies is true also of the minutest micrococci. In 
other words, Dr. Frenzel finds it necessary to assume a general attractive 
force in order to explain the movements of small organisms. 
On the Study of the Movements of Animals. * — Herr B. Fried- 
lander gives some good advice to naturalists and physiologists in regard 
to the hindering of scientific inquiry by the use of words like “ will ” and 
“ instinct.” His essay is a temperate protest against the use of words 
without knowledge, especially in “ explaining ” the movements of 
animals. 
B. INVERTEBRATA. 
Mollusca. 
a. Cephalopoda. 
Cleavage of Ovum in Cephalopods.f — Mr. S. Watase has a memoir 
in which he deals in an extended manner with this subject. Treating, 
first, generally of the animal ovum, he finds an essential fact, viz. that, 
however diverse the examples, they all point to the conclusion that the 
metazoan ovum and its derivates, the tissue-cells, are more than a 
homogeneous, isotropic mass of protoplasm, devoid of definite symmetry. 
As van Beneden points out, the study of caryokinetic figures shows that 
the cell is not only uniaxial, but also bilateral. In several ova which 
have been carefully studied the axes of the caryokinetic figure have been 
seen to correspond in a definite way with the recognizable axes of a 
given ovum, the external shape of which is chiefly determined by the 
quantity and distribution of the food-yolk. The axes thus determined 
are maintained through the different stages of growth, and give rise to 
definite axes of the larval or of the adult organism. 
Dealing next with the relation of the external phenomena of cleavage 
of the ovum to the internal phenomena or caryokinesis, he observes that 
(1) the interzonal portion of the caryokinetic figure consists of a bundle 
of filamentous substance; (2) this substance is essentially the same as 
the archiplasmic filaments of the spindle; (8) the length of these 
filaments is exactly the same as the space between the parallel bands of 
chromosomes in all stages ; (4) the archiplasmic filaments grow in length 
from the poles towards the equator of the nucleus : and (5) the inter- 
zonal filaments come into existence exactly at the moment when the 
single equatorial “ plate ” divides into two parallel daughter “ plates.” 
It seems, therefore, to be probable that after the archiplasmic filaments 
from the two centres have reduced the chromatic contents of the nucleus 
into a flat “ plate ” by gradual lengthening, they continue to grow in 
the same manner, and push through between each other, just as would 
brushes if their ends were pushed together. Two opposing systems of 
the archiplasmic filaments behaving in a similar way, and lengthening 
in a contrary direction, would reduce the spherical nucleus first to a 
biconcave disc, then to a flat “ plate,” and, finally, into two parallel 
* Biol. Centralbl., xi. (1891) pp. 417-29. 
t Journal of Morphology, iv. (1891) pp. 247-302 (4 pis.). 
