Picture - Cosmic Polymath

390 DESIGN IN NATURE
PLATE XO
Plate xc. illustrates development in the bird, fish, and mammal.
Fig i._A. Egg of fowl at early stage of incubation. Sliows unformed body of chick (a), with area vasculosa (h) extending
on either side and partly covering the vitellus (c) ;
^ , ,
B The same further advanced. Head and body of chick (a) becoming defined ; the body being developed by amnion at 6, and
all being bounded by the twisted chalaziferous membrane {d,d').
bavins the umbilical vesicle (d) depending from its under surface. The vascular allantois curves out from the under surface of the
body, and spreads above it like an umbrella (c). The allantois acts as a lung to the chick, and the umbilical vesicle as a, stomach
(after Dalton).
Flu. 2.—Egg of fish, showing the circulation in the vitellus or yolk (Dalton).
Pig. .3.—Young fish, showing formation of umbilical vesicle.
A. Vesicle seen depending as an open sac from ventral surface. Contains the food of the young fash.
B. Umbilical vesicle more closed and communicating with future alimentary canal.
C. Umbilical vesicle of human embryo at fifth week (after Dalton).
Fig. 4.—a. Impregnated egg of fowl with allantois completed, a, Umbilical vesicle ; h, amnion c, allantois.
;
B. The same further advanced ; alimentary canal beginning to make its appearance.