330 



THE ANATOMY OF INVERTEBRATED ANIMALS. 



vided with only three pairs of ambulatory limbs, the fourth 

 pair making its appearance only after ecdysis has occurred. 



Fig. 90. — Ixodes vicinus, female (after Pa-jenstecher').— a, mandibular booklets; &, 

 d, e, fourth, third, and second joints of llie palp ; c, hooklets of sternal surface of 

 proboscis ; /; base of the proboscis ; g, stigma ; h, genital aperture ; i, anal 

 valves. 



In some Acarina^ a singular kind of metamorphosis 

 occurs. 



Thus, in Atax JBoJizi, Claparede ^ observed that, before 

 the limbs appear on the blastoderm, a chitinous cuticula is 

 separated and forms an envelope, which he terms the '*sac 

 of the deutovum." The proper vitelline membrane bursts 

 into two halves, much as in Limulus, and the deutovum 

 emerges. In the mean while, the anterior end of the blasto- 

 derm becomes fashioned into two procephalic lobes ; while 

 five pairs of tubercles, answering to the rudiments of the 

 chelicercTe, pedipalpi, the two posterior gnathites, and one 



1 " Anatomic der Milben," 1860. 



2 " Studien an Acariden." {Zeitschriftfur wiss. Zoologie^ 1868.) 



