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Windows on Life

by Marlys McCurdy

This is a protocol for windowing live fertilized chicken eggs to allow the student to observe living development in action. Students open the egg at approximately 72 hours after incubation has begun. They can open the eggs and make observations for several days using this technique. This protocol was developed in conjunction with research done at Idaho State University in Dr. Trent Stephens lab.

Supplies

  • Fertile chicken eggs - local supplier (check the organic grocery)

  • Chicken Ringer's Solution with antibiotics (avl. from synoptic supply houses for less than $20.00 a liter)

  • Fine-tipped forceps and dissecting scissors

  • Sterile alcohol swabs

  • Sterile 10 cc. syringes with 18 gauge needles

  • Transparent tape

  • Cardboard egg cartons or trays

  • Incubator

Procedure

Allow a full 45-50 minute block of time for the first day and 15 minutes for each day of observation.

  1. Eggs need to be incubated 72 hours to allow embryo to develop to enough for students to see the heart chambers and pumping action. Eggs may be kept at room temperature for several days prior to incubating. Start timing when they are placed in the incubator. This allows you to plan the day you want to start. Do not turn eggs. You want the embryo at the top of the egg.

  2. Have all scissors and forceps soaking in alcohol. Be sure that they are air-dried prior to using on the egg because the alcohol will kill the embryo if dripped in the egg.

  3. Swab the narrow end of the egg with an alcohol wipe and remove 5cc of albumin by carefully inserting the 18 gauge needle on the syringe into the narrow end of the egg with the needle tipped at a sharp angle to avoid the yolk. This is to drop the embryo away from the surface you will open.

  4. Swab the top of the egg. Secure it in a nest of paper towels in a dish or bowl of some kind to keep it from rolling. Gently open the top of the egg with the tip of the forceps or tip of the scissors. Then remove enough egg shell to have an opening 1.5cm X 2.0cm. The eggshell may be ragged but be sure the membrane inside the shell does not fall down and touch the embryo. This tends to "wick dry" the embryo during incubation.

  5. Drip 5-6 drops of room temperature Ringer's solution with antibiotics onto the surface of the yolk not directly on the embryo. Do this with a sterile syringe with no needle attached. Observe the embryo. This is best done with a stereoscope. Don't allow more than 15 minutes observation time. Have students draw the embryo and attempt to label the landmarks. At 72 hours you will have a heart with chambers, limb primordia, somites, head, optic cup and nerve cord.

  6. After observing. Have students cover the opening with transparent tape. It is sterile on the roll and if they do not touch it on the adhesive side, will serve as a sterile patch. Be sure they run a fingernail over the tape on the outside to seal the egg completely. If their hole is too wide use two pieces of tape and use a fingernail to be sure that the two pieces adhere to each other.

  7. Successive days the tape may be opened with sterile scissors and a new layer of tape applied over the old tape after observations. DO NOT ATTEMPT TO REMOVE TAPE FROM EGG SHELL!! Additional Ringer's solution should be dripped in daily as soon as the egg is opened. Again limit your observation time to 15 minutes.

Alternative Procedure

I have an alternative method for windowing that uses clear plastic wrap, PVC pipe and petri dish lids. The survival rate is lower but the observation time is continuous. If you would like a copy of this protocol, please email me at mmccurdy@nicoh.com and I will be happy to send you a copy.

NOTE: A word about vertebrate use in the classroom

I know there is a controversy about the use of live vertebrates in the classroom. I have done this lab for many years with sophomores and seniors in various biology classes. It is always a very popular lab and I use it to generate discussion about the use of live animals in the classroom in addition to teaching embryology. Students have come back after years away from high school and still remember this activity.

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