24 THE WONDER OF LIFE 



devices. We say ' armour ', and we see armadillos in their 

 bony mail, giant sloths with shields an inch in thickness, 

 tortoises almost invulnerable, scale-clad fishes, molluscs 

 in their shells, crustaceans and insects within their strong 

 chitinous cuticles, sea-urchins bristling with heavy spines 

 like hedgehogs, the stage is full of men at arms. 



We think of ' weapons ', and what a collection rises into 

 view, from the microscopic stinging threads of the jelly- 

 fish and the Portuguese man of war to the tusk of the male 

 narwhal, ten feet long, from the forceps of crabs to the 

 antlers of stags, from the stings of bees to the fangs of the 

 cobra, from the lashing tail of the sting-ray to the sword 

 of the sword-fish, from the strangling arms of the octopus 

 to the talons of the eagle ! 



But stopping an endless catalogue, let us take three or 

 four instances of the quaintness of methods of offence and 

 defence. 



In the case of the common nettle, the sting is effected by 

 specialized hairs, each of which shows a bulbous base with 

 glandular cells, a slender stalk with a duct running up it, 

 and a sharp-pointed ' cap ' at the end of the brittle tip. The 

 sharp tip pierces the skin, and in breaking off there effects 

 an injection of the poisonous secretion. In the hair of 

 the Chilian nettle (Loasa) there is no cap to the hair, the 

 tip is sharp-pointed and like a curved needle. 



A very curious means of defence is seen in a number of 

 Holothurians, or sea-cucumbers, which discharge long 

 glutinous threads, or ' Cuvierian organs ' from the posterior 

 end of the body. In Holoihuria nigra, the Cuvierian organs 

 are white conical bodies which are protruded posteriorly, 

 when the creature is irritated. They remain attached by 

 their bases to the animal, but elongate into long glutinous 



