266 COMPARATIVE ANATOMY AND PHYSIOLOGY.- 



bite their victim before injecting the poison ; though, 

 as in the case of the Tarantula, the ill effects of their 

 venom have been somewhat exaggerated, there is no 

 doubt that the poison of many spiders is capable of 

 inflicting mortal injuries; the statement that the 

 West Indian My gale avicularia is able to catch and 

 kill small birds appears to be true. In the Scorpions 

 the poison glands, which are oval in form, and have 

 an outer layer of muscular tissue, are situated in 

 the terminal segment of the body ; their ducts open 

 at the tip of the spinous process at the end of the tail, 

 which is recurved when the animal strikes a blow. 

 Among insects, many of the Hymenoptera are pro- 

 vided with racemose organs placed in the hinder part 

 of the body, which secrete a fluid, the irritating 

 effects of which appear to be due to the contained 

 formic acid ; the venom is injected by a sting, which 

 consists of a median piece grooved longitudinally, and 

 of two side pieces which, on becoming closely applied 

 to it, convert the groove into a capillary canal along 

 which the fluid flows. The venom is not always used 

 merely as a means of offence, many Hymenoptera 

 stinging other insects for the purpose of paralysing 

 them while they carry them to their young, to which 

 they will serve as food. 



Various Fishes are provided with defensive organs 

 possessing venomous properties ; such are the dorsal 

 spines of the weavers, which are deeply grooved and 

 charged with fluid mucus. In Synanceia the free half 

 of each dorsal spine bears a pear-shaped bag in which 

 the milky poison is contained. In Thalassophryne, 

 from Panama, the sac is placed at the base of the 

 spine, and as it is without any muscular sheath, the 

 poison can only be ejected by the pressure exerted on 

 the sac when the spine enters the body (Giinther). 

 The integument of many Amphibia is richly pro- 

 vided with glands, which secrete a viscid fluid possessed 



