11 day old Chick staining (Part 2)

This is Part 2 of the Chick Embryo staining. This chick embryo was incubated for 11 days before it was euthanized ethically. The chick embryo was then placed in Alcian Blue staining solution to dye for cartilage. See 9 Day old Chick Embryo (Part 1) for reference to the protocol. 

Next, I will place the embryo in Alizarin Red to visualize where the cartilage is starting to ossify.

Forelimb of a chick embryo (right lateral view)

Clavicle, sternum and right forelimb of the chick embryo (right lateral view)

Below is the chick embryo's "wrist" and metacarpals. 

Right forelimb of the chick embryo (superior-lateral view)

Here is a composite of 5 images of the spine, from the base of the skull to the tip of the tail.

Vertebral column of a chick embryo (dorsal view). This image has been Photoshopped to merge the images.

Here is a close up of the head, jaw and eyes.

Chick embryo head, future beak and eyes (frontal lateral view)

Here is a view of the os coxae, or hip bones.

Os coxae of the chick embryo (dorsal view)

I disarticulated the hindlimb in order to photograph it better.

Hindlimb of a chick embryo, including the femur, tibia and fibula, and foot (right lateral view)

Below is the right lower leg, including the tibia and fibula.The fibula cartilagedoes not fully extend to the foot. The distal tip of the fibula (lateral malleolus) is referred to as the ankle.

Developing tibia and fibula of a chick embryo (ventral view)

Here is a close-up of the future ankle. There was a ball of condensed cartilage at the interesection of the tibia and metatarsals.

Distal tibia and metatarsals of the foot of a chick embryo (frontal view)

Here are the caudal vertebrae of the chick embryo.

Caudal vertebrae of the chick embryo (right lateral view)

Below are the cervical vertebrae and some thoracic vertebrae.

Cervical and thoracic vertebrae of the chick embryo (right lateral view)

 

The ribcage disarticulated during the staining process, perhaps because the KOH should be at a lower concentration. Regardless, you can see cartilage condensations forming between the ribs. In addition, the cartilage pre-cursors of the vertebrae are already articulating with the rib at 2 points (forming a triangle shape). The rib will articulate with the 2 facets on its corresponding vertebra.

Thoracic vertebrae and ribs of the chick embryo (dorsal view)

There has been a long history of the use of comparative anatomy to provide evidence of evolutionary processes. This methodology has offered insights, although many conceptual errors. The ideas of transformationism, intelligent action and recapitulation each contributed to confusion surrounding evolution.

For millennia, anatomy was the main evidence people had access to for understanding evolutionary phenomena. Researchers in the late 19th century began to see embryology as another source of information for inferring the natural history of species. Embryology later began to raise intriguing, but confusing questions on evolution.

While there have been many errors with this kind of thinking, such as Haeckel's ontogeny-phylogeny argument or the still controversial phylotypic period, one thing is clear, that development plays an important role in evolution. Using comparative methods for anatomy and embryology in tandem can provide insight into evolution. Furthermore in development, we see evidence of evolution.

Before the emergence of genomic technology, comparative anatomy and embryology were the sole modes for reconstructing phylogeny. However, in the 21st century, genome sequencing and molecular techniques began to offer novel insights and sometimes unexpected results about the evolution of vertebrates. Morphological evolution can stem from many mechanisms, including random mutation, changes to protein-coding regions and gene duplication events. But there is one mechanism in particular that merits a close inspection; the role of development in evolution. The natural phenomena, or the morphological consequences, can stem from underlying changes in development.

With our new perspectives, it is time to revisit some of the long-standing questions on the usefulness of using anatomy and embryology. Now that we have molecular evidence can we compare evolution, on several levels simultaneously (via anatomy, genetics, embryology) in order to bear upon some of the long-standing mysteries of phenotypic evolution.

References

Agassiz, L. (1849). Twelve lectures on comparative embryology: delivered before the Lowell Institute, in Boston, December and January, 1848-9. Dewitt & Davenport.

Russell, E. S. (1917). Form and function: A contribution to the history of animal morphology. EP Dutton.

All embryos were treated ethically according to IUCAC protocol.

 


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