ARACHNIDA 461 



which furnish the viscid fluid which covers them. The egg cocoon is 

 formed by the tubuliform glands and these glands are absent in the 

 males. The aciniform glands manufacture the cords which are wrapped 

 round the prey caught in a web, and the pyriform glands make the 

 attachment discs by which a silk thread is anchored to the ground. 

 Such a spider as this is well adapted for its sedentary life in a web. It 

 has immensely long legs compared to the size of the body and on the 

 ground moves slowly and uncertainly. But its legs end in claws and 

 spines, by which it not only can cling with absolute safety to the elastic 

 threads of the web, but which it also uses to weave the threads of silk 

 as they come out of the spinnerets. Thus the web spinners represent 

 the greatest specialization of the group; there are, however, other 

 forms like the wolf spiders (Lycosidae) and the jumping spiders 

 (Salticidae), which are just as predaceous as the Epeiridae but by no 

 means so sedentary. They run swiftly after their prey or jump 

 suddenly on it. They may only possess two ampulliform glands which 

 secrete a "drag line" which they leave behind them as they move. 

 The web spinner relies almost entirely on its sense of touch and 

 the vibration of the lines of the web affecting the tactile hairs of the 

 limbs is the guide to the entangled prey. Eyes, though present, are 

 not efficient. But the hunting spiders find their victims by sight and 

 have a remarkable range of vision. This is not only used in the pursuit 

 of food but also in the elaborate courtships which are characteristic of 

 these two families, during which the male executes the most fantastic 

 dances. 



The generative apertures are found between the aperture of the 

 anterior pair of lung books and the spinnerets. Fertilization is internal 

 and before the male is ready to fertilize the female the sperm must be 

 transferred to his modified pedipalps (Fig. 338). The terminal joint 

 of these is greatly enlarged and contains a complicated tubular vesicular 

 seminalis. A drop of seminal fluid is emitted either on to a small web 

 spun by the male or on some surface like a leaf and the palps are then 

 applied to the fluid and the seminal vesicle charged. After this court- 

 ship begins, and at the close the palps are inserted into the genital 

 opening of the female; the spermatozoa are stored in spermathecae. 

 The eggs are laid in a cocoon. 



Class ACARINA (Mites and ticks) 



Arachnids with a rounded body with no boundary between the 

 prosoma and the opisthosoma ; basal segments of the pedipalps united 

 behind the mouth; no gnathobases to the four walking limbs. 



These forms are usually minute except in the case of the parasitic 

 ticks. They are, variously, scavengers, ectoparasites on all sorts of 



