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. 



Fia. 90. — Ixodes vicinus, female (after Pajfenstecher*).— a, mandibular booklets ; ft, 

 d, e, fourth, third, and seccmd joints of the palp ; c, booklets of sternal surface of 

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

 valves. 



In some A.carina, a singular kind of metamorphosis 

 occurs. 



Thus, in Atax JBonzi, Clapar^de ^ 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 

 chelicer.ie, pedipalpi, the two posterior gnathites, and one 



» " Anatomie der Milben," 18«0. 



3 " Studien an Acariden." (Zdtschrift fiir wiss. Zoologie^ 1868.) 



