1060 The American Naturalist. [December, 
Moving pigment in Eggs.—In a carefully illustrated account’ of 
the cleavage of the Planarian, Polycherus caudatus Mark, Dr. E. G. 
Gardiner describes most remarkable changes in position of peculiar, 
algalike, pigment bodies which color the eggs orange-red for a certain 
period. These bodies appear in certain cells and then others, they lie 
along the lines where cleavage is to take place. 
They move up from the centre of the egg to the surface and move 
from place to place. 
Fertilization.—By the use of nitric acid Kostanecki and Wierze- 
jski find that the so-called achromatic substance may be demonstrated 
with remarkable clearness in the eggs of the pond snail Physa fontinalis. 
In a detailed description‘ of radiations, or stars, of this substance seen 
during the process of maturation of the egg and during fertilization, 
illustrated by many remarkable figures of reconstructed sections, the 
authors give the facts that lead them toward the following hypothetical 
conception of the true nature of the process of fertilization. 
The object of fertilization is the union of the nuclei; but the neces- 
ary condition to make this of avail is that the egg be able to continue 
to divide, to undergo cleavage. This power is brought to it by the new 
nuclear part of the sperm. 
Each sexual cell needs to be supplemented by what the other has and 
it itself is deficient in. This lack is in the protoplasm. 
The egg has large amounts of nutritive material while the sperm has 
none. The former has thus relatively too little protoplasm to continue 
dividing by itself. During maturation, by dividing twice to form polar 
bodies, the egg uses up its remaining power of division and must have 
this added to it again if it is to cleave at all. 
What the sperm brings in to replace the exhausted cleaving powers 
of the egg is the connecting piece of the sperm, the portion near the 
head or nucleus, that contains achromatic material centered on the 
centrosome or speck next the head. This material isthe remnant from 
the achromatic figure of the last cell division in the formation of sperms. 
This material is conceived of as concentrated and not, as yet, recog- 
nized till it gets into the egg; then it swells up and extend in radii as 
an umbrella unfolds. As the sperm revolves through 180° after enter- 
ing the egg the middle piece preceeds the sperm head or male nucleus 
in its journey towards the female nucleus. The middle piece appears as 
a star centered about the centrosome and rapidly grows in all direction 
3 Journal of Morphology, XI, pp. 155-171. 
t Archiv. f. Mik. Anat., 47, 2, Apl , 1896, pps. 309--379, Pls. 18--2). 
