846 CLASS V. ARACHNIDA. 



ventral nerve cord. The sense organs are eyes but these are 

 not always present. Sensory hairs also exist and with these may 

 be grouped the pseudostigmatic organs of the Oribatidae which 

 protrude from sockets on the dorsal side of the cephalothorax. 



The reproductive organs (Fig. 557) are typically annular and 

 much alike in both sexes. The two testes are fused, and each opens 



J?IG. 557. a Male ; 6 female genital organs of a Mite Argas (after Al. Pagenstecher). T 

 Testes ; Vd seminal duct ; Dr prostate gland ; Go genital opening ; Ov ovaries ; Od oviduct ; 

 U uterus ; Dr glandular appendages. 



into a vas deferens. These unite at the external opening which lies 

 in the ventral middle line, usually between the last pair of legs, 

 but it may be shifted even more anteriorly. The male often 

 bears a pair of suckers near the posterior end of the body and 

 in many genera there is an intromittent organ. In some cases 

 where this is absent the chelicerae deposit the spermatophore 

 at the genital opening of the female in something the same way 

 as the pedipalpi do in spiders. The ovaries are fused and their 

 oviducts unite into a uterus or vagina whose opening corresponds 

 in position with that of the males. An ovipositor may be 

 present. 



Mites undergo a metamorphosis (Fig. 558) and pass through 

 several instars before becoming adult, but the stages are not the 

 same in all species. The first is the egg which is usually undeveloped 

 at oviposition, but in some of the Oribatidae is almost ready for 

 hatching. The second is the deutovum which occurs for instance 

 in Atax ; here an outer eggshell becomes hard and brown and 

 then splits longitudinally, thus allowing for the growth of the 

 larva whilst at the same time affording it some protection. The 



