The Egg

The boys' grandmother (mor mor = literally mother's mother in Norwegian) arrived yesterday. They always get to choose a little present of some description and Todd opted for a Dino Magic egg. The idea is a good one - you unwrap the egg and place it into warm water, this triggers a chemical reaction and, after some fizzing and bubbling, the model dinosaur is revealed. There are 28 to collect and these are split into 4 categories:- common, uncommon, rare and ultra rare. Todd did well with his first selection and managed to land a rare Postosuchus. 

This little toy allowed us to discuss chemical reactions and reinforce an already excellent knowledge on population densities and extinction. Not a bad choice all in all. But perhaps the most poignant discussion, when considering this effervescent treat, is the very miracle that is an egg. 

We can categorise reproduction in four main ways:

Viviparity - nutrients are provided by the mother, often via a placenta.

Oviparity - internal fertilisation occurs and the mother lays eggs e.g birds

Ovuliparity - external fertilisation occurs and the young hatch from eggs e.g most frogs

Ovoviviparity - internal fertilisation and the eggs are retained in the female's (or male's in the case of seahorses) body until they are ready to hatch. They enter the world as fully formed, live young.

Let's focus on the reproductive modes associated with external egg laying - Ovuliparity and Oviparity. Most frogs and all birds utilise these methods. I am sure not many people exited childhood without ever noticing (or deliberately seeking we hope) the reams upon reams of spawn that fill even the tiniest of ponds in early spring. Likewise we only have to enter a supermarket to gain an appreciation of the ovum structure developed inside the bodies of our feathered friends. 

Amphibian's are closely tied to water and cannot successfully reproduce without it. The delicate swathes of jelly, which encase and protect their fragile inky-black beacons of life, will quickly dessicate if removed from water for any length of time. Amphibian spawn doesn't need much water to facilitate  successful hatching of offspring, in fact some species can utilise little more than a puddle nestled inside a leaf, but remove it completely and it is game over. 

Birds, on the other hand, have evolved to produce eggs with solid shells and rigid structures. This ensures they do not require an aqueous environment and can survive far more severe, fluctuating conditions, but it also means they break easily if dropped from a height. As with most things in life there is a trade off. Bird eggs may appear completely sealed to the naked eye, but they are covered in microscopic holes, which facilitate gaseous exchange and connect the egg directly with the world outside. These minute pores mean a bird egg dropped in water for a prolonged period is doomed to failure, unlike our artifical dino egg, which requires water in order to successfully release its cargo!

As a child I bred jewelled lizards and far more recently I hatched a couple of Storr's monitor lizards (V.storri storri).

Unfortunately a faulty digital thermometer doomed five of the eggs to failure, but the two that made it went on to become strong, active little creatures. Leo was too young to remember much about the event, but Todd excitedly observed one pulling itself free of the white, leathery prison and venturing into the unknown. Looking at those eggs it was hard to believe they could contain 4" baby lizards, but an egg is a miraculous thing. Little more than a leathery shell, albumen (white) and yolk, the egg completes its task as an external vehicle for life - assuming the conditions stay within certain limits. 

Behold a baby Storr's monitor lizard! Miraculous, especially when the thermometer was reading 4 degrees C lower than the true temperature. I was lucky any made it at all, but here we saw that other cliche of life, one which rings true whether brought into this world through viviparity or oviparity - only the strongest survive to take their genes further.