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A ligature placed either around the junction between the sinus venosus and atrium of the frog or turtle heart (first stannius ligature) or around the atrioventricular junction (second stannius ligature); demonstrates that the cardiac impulse is conducted from sinus venosus to atria to ventricle, but that successive chambers possess automaticity ...
Gastrulation then continues along the ventroposterior blastopore lip and posterior streak region, from where cells contribute to ventral and posterior mesoderm. Adding to this, Brachyury and caudal homologues are expressed circumferentially around the blastopore lips in the frog, and along the primitive streak in chick and mouse. This would ...
The blastula develops into a structure called a gastrula through a process called gastrulation. The gastrula then undergoes further development, including the formation of organs ( organogenesis ). The embryo then transforms into the next stage of development, the nature of which varies among different animal species (examples of possible next ...
Before gastrulation, the embryo is a continuous epithelial sheet of cells; by the end of gastrulation, the embryo has begun differentiation to establish distinct cell lineages, set up the basic axes of the body (e.g. dorsal–ventral, anterior–posterior), and internalized one or more cell types including the prospective gut. [2]
In the frog Xenopus laevis, the animal pole is heavily pigmented while the vegetal pole remains unpigmented. [4] A pigment pattern provides the oocyte with features of a radially symmetrical body with a distinct polarity. The animal hemisphere is dark brown, and the vegetal hemisphere is only weakly pigmented.
The world's largest frog is the goliath frog of West Africa—it can grow to 15 inches (38 centimeters) and weigh up to 7 pounds (3.2 kilograms). One of the smallest is the Cuban tree toad, which ...
A typical frog embryo, incubated at 18 °C, is an early stage neurula by 50 hours post-fertilization and a late stage neurula by 67 hours. [3] The mouse embryo begins neurulation on day 7.5 of gestation and remains in the neurula stage until day 9.
Invagination of the archenteron during sea urchin gastrulation. Sea urchin gastrulation is another classic model for invagination in embryology. One of the early gastrulation movements in sea urchins is the invagination of a region of cells at the vegetal side of the embryo (vegetal plate) to become the archenteron, or future gut tube. There ...