224 GENERAL ORNITHOLOGY. 
the eggs of all birds vary more in size and shayi@han some of the devotees of theoretical odlogy 
admit in their practice. The variation so well known in any breed of domestic fowl is scarcely 
above a normal rate. The short diameter, corresponding to the calibre of the oviduct, is less 
variable than the long axis; for when the quantity of food-yelk and white, upon which the 
difference in bulk depends, varies with the vigor of the individual, the scantiness or redundancy 
is expressed by the shortening or lengthening of the whole mass. The egg traverses the 
passage small end foremost, like a round wedge, with obvious reference to ease of parturition 
by more gradual dilatation of the outlet. 
Germination. — Leaving now all the accessory parts of an egg, let us confine attention 
to the germ-yelk, or ** tread,” which is alone concerned in the germinative process. Recurring 
to the female Dynamameba, consisting of granular protoplasm (vitellus) included in its cell- 
wall (vitelline membrane) and including its nucleus and nucleolus (germinal vesicle and germi- 
nal spot), we will trace it up to the time it begins to take shape as an embryochick. At first, 
as I have observed before, it is like any other amceba; the first step of development is prob- 
ably a retrograde one; for if there ensues, when the spermatozoa melt into the ovum, the 
result affirmed for mammalian ova, the original germinal vesicle and germinal spot disappear, 
and the whole con- 
tent of the ovum 
proper is simply a 
homogeneous mass 
of granular proto- 
plasm. In this ret~ 
rograde step, the or- 
ganism, at the low- 
est possible round 
of the ladder of 
evolution, is called 
a monerula. The 
germinal __ vesicle 
and spot, however, 
are speedily recon- 
structed, and the 
ovum looks pre- 
cisely as it did be- 
Fi. 111. — Segmentation of the vitellus by disesidal cleavage, diagrammatic, x about fore. But observe 
10 times, after Haeckel. Only the *‘tread,” cicatricle, or germ-yelk (figs. 109, 6,110, 4)is that the actual dif- 
represented, as no other part of the whole yelk-ball undergoes the process. A, separation icnerbe is : 
into 2; B, into 4; C, into 16, by 8 radial and 1 concentric furrow; ), into many parts, by erence 1s COLMOUS; 
16 radial and about 4 concentric furrows: ZF, 64 radial and about 6 concentric furrows; for it now consists 
F, the whole tread broken up into a mulberry-mass (morw/q) of cells. 
: 4 y of the blended sub- 
stance of the original oyum and of the spermatozoa; and in this duplex or bisexed state, 
before any further step is taken, the creature is called a cytula,—the parent cell of the entire 
future organism. In the former state it could reproduce nothing, not even itself; for it is the 
strange physiological law of a Dynamameba that it cannot reproduce like an ordinary cell, 
but must evolve an entire organism, like both of those two whose vital forces it concentrates, 
summarizes, and embodies, — or nothing. 
The first change in the parent-cell is that by which it becomes broken up into a mass of 
cells, each of which is just like itself. This process is called segmentation of the vitellus; each 
one of the numerous resulting cells is called a cleavage-cell. The nucleus of the parent-cell 
ivides into two; each attracts its half of the yelk; the halves furrow apart and there are now 
