ACTIVE DEFENCE 357 



is injected into the wound by the pressure of the foot on the 

 poison-bags. Death has not rarely been the result." Two of our 

 native sea-fishes, the Greater and Lesser Weevers iyTrachinus 

 draco and T. vipera) are poisonous to a less extent, being pro- 

 vided with grooved spines on the back and operculum. There 

 are here no poison-bags, but the slime which covers the spines 

 has venomous properties. 



Among Elasmobranchs, the Sting- Rays {Tryg07udcs) and Eagle- 

 Rays iyMyliobatidce) commonly possess one or more saw-edwed 

 spines on the tail, by the lashing movements of which they can 

 be used to inflict jagged wounds, these injuries being at the same 

 time rendered more dangerous by the poisonous nature of the slime 

 which covers the spines. The range of one species, the Common 

 Sting-Ray [Trygon pastinacd), includes the south coast of England. 



Actively Defensive Weapons of Mollusca. — In the tropical 

 Cone- Shells the horny ribbon of the rasping organ bears barbed 

 teeth, upon each of which a poison-gland opens (p. 97). The 

 living animal requires careful handling, for it promptly makes use 

 of its means of defence. Another arrano-ement is found in some of 



o 



those Sea-Slugs (species of yEolis) in which a number of club- 

 shaped outgrowths {ceratd) spring from the back, for these struc- 

 tures are armed with sting-ino-cells much like those characteristic 

 of jelly-fishes, sea-anemones, &c. 



In some of the large Bivalve Molluscs the mere closing of the 

 shell constitutes a defence which may prove fatal to an attacking 

 animal. A good example of this is given by Semon (in In the 

 Aitstralian Bush), where, in speaking of the natural history of 

 Torres Straits, he says: — "A certain precaution has to be observed 

 when collecting on the reefs. In the shallow water lie, their sides 

 unfolded, the gigantic Tridacna-shells, such as are sometimes used 

 in Europe as a font for holy water in Catholic churches, or as 

 ornaments in halls and gardens. Woe to him who, in wading 

 through the water, carelessly touches one of them. Many a 

 searcher of tripang has met with this accident, and has had his 

 foot cut through to the bone by the shells, which shut up with 

 enormous force. No human power can open the shell, and a 

 man thus caught can only be relieved by his companions cutting 

 the adductor muscles of the shell with a knife." 



Actively Defensive Weapons of Insects. — The most formidable 

 structure calling for description here is the sting with which the 



