THE FORMATION OP THE LARVAL INTEGUMENTS. 



99 



embryo (or larva) continues to develop, surrounded only by the 

 cuticular deutovum (Figs. 52 and 53, A and B). The limbs only 

 now become jointed, the eyes appear, and the inner organisation 

 becomes perfected (Fig. 53 B). 



The eggs of Atax Bonzi are usually laid on the gills of the Lamelli- 

 branch (Unio) in which this Acarid lives for a portion of its life. 

 When the embryo is sufficiently mature, it breaks through the 

 deutovum and, as a six-limbed larva, passes into the respiratory 

 cavity of its host. The larva of most Acarina lead a free life. 



-ff. 



B. 



-z% 



Fig. 53.— Two stages in the development of the hexapod larva of Atax Bonzi enclosed within 

 the cuticular deutovum (after Clapar£de). au, eye ; ch, chelicerae ; d, yolk ; dm, cuticular 

 deutovum ; Id, cephalic lobe ; p x -p s , three pairs of limbs ; pcd, pedipalps ; r, proboscis 

 (derived chiefly from the chelicerae) ; si, caudal lobes ; z, cells between the body-integument 

 and the outer membrane ("haemamoebae"). 



The formation of larval integuments within the egg recalls the processes which, 

 under similar circumstances, take place in the Crustacea. The early secretion of 

 the cuticular envelopes, as, for instance, in Atax, finds its analogue in the 

 formation of the blastodermic cuticle in many Crustacea. The sac-like envelope 

 recurs in Apus, the embryo of which leaves the egg enclosed in such an envelope, 

 and within it probably passes through part of its development until it reaches 

 the Nauplius stage. There are other Crustacean larval integuments which form 

 •only at a later stage, as in some Acarina, and which are consequently already 

 provided with appendages (c/. Vol. ii., p. 118). 



