376 SYNOPTIC COLLECTION. 



grown, 1 and a mite, Sphaerogyna ventricosa, carries the 

 process still further if it is true that it produces sexually 

 mature animals which are fertilized as soon as born. 2 



It is probable that the parasitic habit of the larva of 

 many species of mites tends to reduce the number of legs 

 in this stage, and this view finds confirmation in the fact 

 that some of the mites of the family Oribatidae which are 

 terrestrial, living in moss, under stones, and the like, are 

 said to have four pairs of legs when hatched.3 



While most mites have four pairs of legs in the adult 

 stage, it is interesting to note that the gall-making species, 

 Phytoptus pyri Scheuten (PI. 934, fig. i), which bores 

 into leaves and lives in the cavities or galls that it makes, 

 has only two pairs of these organs. 



Among the mites, the sea-spiders or Pycnogonida may 

 be placed, though there is a diversity of opinion among 

 naturalists in regard to their true position. Morgan 4 has 

 shown, however, that the younger stages of the Pycnogo- 

 nids tend to prove a relationship with the Arachnida. 

 This group is represented in the Collection by Phoxichi- 

 lidium (No. 935, upper specimens on the tablet) and Pyc- 

 nogonum (No. 935, lower specimens). In these forms 

 the abdomen is a mere vestige, while the anterior part of 

 the body extends forward into a proboscis which is used 

 for sucking. In reality, there is scarcely any body, the 

 animal being almost wholly made up of legs into which 

 extend, apparently of necessity, some of the internal 

 organs. The more typical members of the group, like 

 Nymphon stromi Kroyer (PI. 936, fig. i, <) have besides 

 the proboscis a pair of clawed appendages (fig. i) which 

 are considered antennae by Wilson and mandibles by 



l. 24, Texas Agric. Exper. Sta., 1892, p. 242. 



2 See Shipley, Zool. of the Invert., 1893, p. 420. 



3 See Kingsley, Stand. Nat. Hist., II, 1884, p. 102. 



4 Johns Hopkins Univ., Stud. Biol. Lab., V, no. i, 1891, pp. 

 25-33- 



