Spiders and Their Near Relatives 



Thus in the genus Pteroptus the larval stadium is passed within 

 the body of the mother, and in the genus Pediculoides the young 

 are retained within the body of the mother till they reach the 

 adult stage. And in many there has been developed a peculiar 

 nymphal instar, known as the bypopus (hyp'o-pus), the function 

 of which is the distribution of the species. The hypopus differs 

 greatly in structure from the preceding and the succeeding 

 nymphal instars, both of which have normal legs and mouth- 

 parts. In the hypopus there is no mouth opening and no mouth- 

 parts; and the legs are short and not fitted for walking. On the 

 ventral surface near the tip of the abdomen there is an area pro- 

 vided with several sucking disks by means of which the hypopus 

 attaches itself to an insect or other animal and is transported to 

 some other locality, where it may find a suitable breeding place. 

 When this is reached the hypopus transforms into a normal nymph. 



The order Acarina is one of great biologic interest and of 

 equally great economic importance; but the minute size of most 

 of the species makes its study somewhat difficult, and compara- 

 tively few students are attracted to it. In fact few people realize 

 the immense number of individuals and of species of mites that 

 are about us. In a recent catalogue. Banks ('07) enumerates 

 450 species, representing [33 genera, that are found within the 

 United States. And it is probable that not more than one 

 third of our species have been described. 



It is impractical to treat the Acarina in this work as fullv 

 as are treated the other orders of Arachnida, without greatly 

 exceeding the desirable limits of space. The student who wishes 

 to study this group seriously must make use of more special works. 

 Fortunately a most excellent treatise on the mites of this country 

 has been published by Banks ('04) who has given much attention 

 to the order and who has described many of our known species. 

 In the preparation of the account given here, I have freely used 

 this work by Banks. Among other important American papers 

 is a Review of the Genera of the Water-mites, by Wolcotl ('05); 

 a Revision of the Ixodoidea, or Ticks of the United Slates, by Banks 

 ('08), papers on the Oribatoidea by II. E. F.wing, and studies on 

 the gall-mites are being published by Parrott, Hodgkiss, and 

 Schoene at the Geneva, N. Y., Experiment Station. I here are 

 many European works on this order; the most important is 

 Canestrini's Prospctto dell' Acarofauna Italiana, published at 



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