84 Transactions Texas Academy of Science. — 1906. 
production has been regarded as a radical one, but our explanation 
shows that they have an important act in common, namely, separation 
of germ cells from a parental soma. The idea of a germ cell carrying 
body cells along with it need not appear strange; for the egg of a 
Mammal when it leaves the ovary takes with it the zona radiata, an 
envelope of follicular cells, while the eggs of numerous other forms, 
notably Annelids and Platodes, carry with them one or more nurse 
cells. In asexual reproduction the germ cells are immature, and 
maintain an envelope of different kinds of somatic cells. 
Another resemblance of the two kinds of reproduction may be 
mentioned. Germ cells leave a dying soma, in the process of sexual 
reproduction. Metazoan buds separate from a parent, or residuum, 
that equally dies. One need simply call to mind the process of gem- 
mule formation in Sponges and that of statoblast development in 
Phylactolaemata. Therefore both kinds of reproduction are in a 
sense acts of excretion by the newly arising individual, removal of 
waste products by separation from them, and in both the energies 
of germ cells may play the initial role. 
B. The Life-Cycles of the Metazoa. 
We arrive at one of the most fascinating subjects that it is the 
joy and privilege of the biologist to contemplate — that of the ana- 
lysis of life cycles. But we may not rush at once in medias res, but 
rather approach the subject from the side of the relation of germ- 
inal to somatic cycles. In our present scanty knowledge of the 
phenomena the following thoughts can be considered little more than 
tentative. 
The mature egg is the beginning of the new individual, and early 
in its cleavage comes the point of divergence of germ and body cells. 
Thence proceeds that division of labor of the multiplying cells that 
we know as their differentiation. But all cells of the germinal cycle 
do not become functional reproductive or fertilizing elements, how- 
ever, for here, too, is a division of labor in that some germ cells be- 
come in a sense retarded and do not reach germinal maturity. Such 
retarded cells become primarily devoted to the mechanical protec- 
tion and nutrition of their brethren; they are the cells of Sertoli 
in the testis, the follicular, nutritive and yolk-forming cells in the 
ovary. Different animals exhibit a great diversity of these, and 
every germ gland contains some kind of them. Physiologically they 
may be considered germ cells that have been overmastered by the 
other germ cells in the struggle for food. In their most primitive 
arrangement the germ cells are more or less dispersed, due sometimes 
to automatic locomotion. This diffuseness probably remains through 
