70 Gen. Sub. i. general subjects. 
(fibres, threads, cords, tubules), in. In protoplasmic layers, iv. In pro- 
toplasmic masses. Processes are classified as (a) taxic (free, migratory, 
or flowing) ; ( b ) tropic (turning of protoplasmic bodies in different 
directions) ; and (c) general growth processes ; Davenport (138). 
Conditions of development. Fundamental properties of protoplasm. 
Individuality and division of labour. Environmental influence on form, 
heredity, Ac.; Pfeffee (523). — Growth and differentiation, mathematical 
analysis of the process ; Brucker (80). — Gradual loss of many-sidedness 
on the part of the somatic cells ; in the course of differentiating cell- 
division, functions and potentialities are restricted. This restriction is 
in proportion to the grade of phyletic and ontogenetic development ; 
Nussbaum. (495). — Aggregation and differentiation; Cattaneo (95). — 
Embryological criterion of homologies ; Wilson (760a). 
Recapitulation : — Sedgwick’s emphasis on embryonic phases as an aid 
to phylogenetic theory. The earliest well-marked larval stage is the 
blastula. The ancestral blastula was presumably uniform. But move- 
ment in a definite direction would result in elongated form. The pos- 
terior cells, least suited for locomotion, and best situated for catching 
food- particles, become specially digestive. An increase in number, if the 
form of the colony be retained, involves invagination. Anterior cells, 
most stimulated, become specially sensitive ; MacBride (416). — Oppo- 
sition to the recapitulation doctrine ; Beard (26). — The recapitulation 
doctrine scarcely half true ; Minot (449). — Embryo and larva, the differ- 
ence between them, and its meaning ; Minot (449). — Periodicity in 
cleavages of Nematode ovum ; Ziegler (770). — What is a germinal layer ? 
History of opinion. Difficulty of establishing a homology throughout. 
The morphological and physiological conceptions of a germinal layer are 
often confused ; Braem (63). — Homology of the germinal layers ; Ciiun 
(107). — Formation of the germinal layers in Vertebrata ; Samassa (617, 619). 
Evolution of embryonic functions, respiration; Bakounine (16). 
Particular organs : — The ectoderm and the nervous system; Mitro- 
PHanow (453). — Origin of the peripheral nervous system; Mitrophanow 
(454). — Ectodermic origin of branchial cartilages of Ammocoetes ; von 
Kupffer (369). — Early stages in the development of the head and the 
brain in Vertebrata ; His (311). — Development of the hypophysis; 
Valenti (703). — Discovery of Thymus rudiments in larval Lamprey ; 
four associated with each of the seven branchial sacs ; Sciiaffer (624). — 
Hypochorda of frog, a dorsal constriction from gut, in part composed of 
a series of segmental tubes, eventually degenerating without role ; 
StOiir (670). — Pancreas of frog has three rudiments ; a second dorsal 
process is the root of the Schwanzdarm, and forms nothing. Perhaps the 
alleged fourth rudiment in the sturgeon (v. Kupffer) is of the same 
nature ; StOhr (670, 671).— First stages of the main outgrowths from the 
gut of the frog; Weysse (748).— On cell-lineage of Ascidian egg ; Castle 
(94). — Reversal of cleavage in a sinistral Gasteropod ; Crampton (122). 
