66. The early embryonic development in amphibians and aves serve as two different model plans of development. In the former the germ layer formation is initiated from a fluid-filled ball like blastula, while in the latter the germ layer formation is initiated on a flat blastodisc. Given below are some of the terms for amphibian embryo in column l and from avian embryo in
    column ll:

    Which of the following is the all correct match of the terms in Column l with that of Column ll?
    (1) A-iv, B-iii, C-ii, D-v, E-l (2) A-iv, B-ii, C-iii, D-v, E-i
    (3) A-v, B-i, C-ii, D-iv, E-iii (4) A-i, B-ii, C-iii, D-iv, E-v

The correct matching of terms for embryonic structures between amphibian (Column I) and avian (Column II) embryos is:

(2) A-iv, B-ii, C-iii, D-v, E-i

Explanation of matches:

• A. Blastocoel (amphibian) matches iv. Space between epiblast and hypoblast (avian), as both serve as fluid-filled cavities facilitating cell movement during gastrulation.

• B. Blastopore lip (amphibian), the site of involution during gastrulation, corresponds to ii. Primitive streak (avian), where cells ingress to form mesoderm and endoderm.

• C. Dorsal lip of blastopore (amphibian), the organizer region, matches iii. Hensen’s node (avian), functional equivalents that pattern the embryo.

• D. Blastopore (amphibian) corresponds to v. Primitive groove (avian), the opening for ingression of cells during gastrulation.

• E. Archenteron (amphibian) corresponds to i. Primitive gut (avian), the early gut formed by gastrulation.

Introduction

Amphibian and avian embryos follow distinctive, yet homologous, developmental paths, particularly during gastrulation. While amphibians develop from a fluid-filled, spherical blastula, birds form from a flat blastodisc atop yolk. Despite morphological differences, key structures and processes show evolutionary conservation. Understanding the exact equivalence of terms between these two models illuminates the shared principles of vertebrate embryogenesis.

Key Amphibian Structures and Their Avian Equivalents

• Blastocoel (A) and Space between Epiblast and Hypoblast (iv):
  Both function as fluid-filled cavities facilitating cell movements during gastrulation stages.​

• Blastopore Lip (B) and Primitive Streak (ii):
  The amphibian blastopore lip initiates cell involution and gastrulation. The avian primitive streak serves this role as a visible thickened band where cells ingress.​

• Dorsal Lip of Blastopore (C) and Hensen’s Node (iii):
  The dorsal blastopore lip acts as the organizer in amphibians, equivalent to Hensen’s node in birds—both directing embryonic axis patterning.​

• Blastopore (D) and Primitive Groove (v):
  The blastopore opening in amphibians corresponds to the primitive groove within the primitive streak in birds, guiding cell internalization.​

• Archenteron (E) and Primitive Gut (i):
  The archenteron formed during amphibian gastrulation matches the primitive gut forming post-gastrulation in avian species.​

Evolutionary Implications

• Despite physical differences—a spherical blastula versus a flat disc—the conservation of structures underscores a shared vertebrate developmental plan.​

• Placements in the embryo may shift, but functions like germ layer formation and body axis patterning remain consistent.​

Summary Table: Matching Amphibian and Avian Embryonic Structures

Conclusion

The comparative developmental terminology between amphibian and avian embryos reveals fundamental homologies despite morphological differences. The matched terms in option (2) correctly reflect this conserved embryonic organization, providing a clear framework for understanding vertebrate gastrulation mechanics.