A SKETCH OF HIS LIFE 
27 
budding in Salpa with that in Pyrosoma and in the Clavelinidse 
among the ascidians. The stolon is bilaterally symmetrical, its 
planes of symmetry coinciding with those of the solitary Salpa 
which bears it, and at first the planes of symmetry of every 
member of the chain coincide with those of the stolon and the 
solitary Salpa. Very soon, however, a twisting of the chain occurs 
which leads to the formation of a double row of Salpae, each row 
with the dorsal surfaces of its members turned outward while the 
ventral surfaces of the two rows are turned toward one another, 
and the right sides of the members of one row and the left sides of 
those of the other row are turned toward the base of the stolon. 
He showed that the placenta of Salpa does not resemble the 
mammalian placenta in its method of nourishing the embryo, 
but that certain cells in the placenta, taking nourishment from 
the blood stream of the nurse (the chain Salpa), grow to very 
large size, then lose their connection with the placenta and wander 
to different parts of the embryo, where they break down and nour- 
ish the growing tissues of the embryo. 
Salensky's generally accurate work upon the embryology of 
many species of Salpa contained one fundamental error, since 
he described the embryos as arising not from true blastomeres 
but from follicle cells, the blastomeres degenerating early in the 
developmental history. Brooks, recognizing the improbability 
of any such conditions, succeeded in tracing the development of 
the egg itself until from its blastomeres the organs arise. He found 
that the blastomeres develop very slowly; that the follicle cells, 
on the other hand, proliferate very rapidly and take on the form 
of the rudiments of the several organs, the organs being thus 
blocked out in these extra-embryonic cells, while as yet the blas- 
tomeres are very few in number. Later the blastomeres multiply 
and pass into the diff erent parts of the mold thus formed for them 
by the follicle cells, and gradually use as food the degenerating 
follicle cells that surround them. 
In his latest, unpublished work he traced the cleavage of the 
egg; he found a clear gastrula arising by invagination from the group 
of blastomeres ; he observed the hollow dorsal nerve tube, finding 
it at first considerably elongated; he found a postero-dorsal rod 
