there is not only a " deutovum," but also what Claparede calls a 

 " tritovum-stage," there being two stages with distinct embryonal 

 membranes before the six-legged free larval state is assumed, the 

 larva when hatching having thrown off two membranes, as well as 

 the egg-shell. Certain bird-mites pass through four stages to 

 reach the male condition, while the females pass through as many 

 as five before attaining sexual Fig. aw. 



blance to other mites and are Tick and Six lcgged Youn s- 

 often mistaken for intestinal worms. I refer to the Pentastoma 

 and Linguatula. Here the metamorphosis is backwards, the young 

 after passing through a morula condition, being born as short, 

 plump, oval mites, provided with boring horny jaws, but with only 

 two short rudimentary legs. 



Finally, we come to those problematical forms, the sea-spiders, 

 or Pycnogonidie, which are often referred to the Crustacea, whose 

 development has been so faithfully studied by Dr. Dohrn. The 

 yolk undergoes total segmentation, and the young are hatched 

 with three pairs of legs, which after moulting attain in some spe- 



To sum up, then, certain mites pass through either — 



1. A Morula state, or the yolk only partially divides. 



2. Sometimes one or two embryonal stages (deutovum and 



3. A six-legged larval state. 



4. Eight-legged "pupal" state. 



The water-bears or Tan lignidos 

 are born with four pairs of legs, 

 not undergoing any metamorpho- 

 sis. Not so, however, with cer- 

 tain worm-like mites, which by 



maturity. Fig. 265 illu.-tnitcs 

 the six-legged larva of the tick, 

 which is simply a large mite. The 



one, as in the spiders. 



5. 



