One difference between early development in humans and in Xenopus (frogs) is that _____.
A) in humans, blastocysts implant into the uterine wall; there is no implantation in Xenopus
B) in humans, neurulation occurs immediately after cleavage; in Xenopus, neurulation is delayed
until after gastrulation
C) in humans, there is no formation of the blastula; in Xenopus, the blastula is a critical stage in
D) in humans, the yolk sac is much smaller than that seen in Xenopus
E) in humans, gastrulation is delayed as the egg moves along the fallopian tube; in Xenopus,
gastrulation takes place immediately after blastula formation