676 SCIENCE PROGRESS 



in front of the older ones. Nevertheless, the root of the new 

 spine became directed backward beneath and on each side of the 

 preceding one, so as to embrace it. At first probably the older 

 spines were shed, but in time they began to cohere and thus 

 form a compound spine. In Edestus this was straight or slightly 

 bent. All of it, or nearly all, except the serrated teeth, were 

 buried in the flesh. As more and more elements were added 

 the organ became more curved and finally in some species 

 {Helicoprion and Lissoprion) formed a spiral, which was directed 

 backward and the last turn of the shaft of which was elevated 

 enough to keep the teeth from cutting into the skin. Such a 

 weapon could be brought into action only if its possessor had 

 dived under its victim and brought the spine across its abdomen, 

 thus disembowelling it. It is in this way that the stickleback 

 {Gastrosteus) attacks its enemies." 



These organs are now referred to the four genera Edestus, 

 Toxoprion, Lissoprion, and Helicoprion. In the first the saw is 

 straight or nearly so, in the second the shaft is bent to a certain 

 extent, while in the other two it forms a complete spiral coil. 



