DEVELOPMENT AND IMMATURE STAGES. 131 



represents a leg; Claparede thought that they all 

 represented thoracic segments ; but remarks that they 

 are worth investigation because in the fully-formed 

 creature only one furrow remained, and that was 

 between the second and third pairs of legs (this furrow 

 modern acarologists usually consider to be the demar- 

 cation between cephalothorax and abdomen). 



The mandibular and maxillary knobs now undergo a 

 process of fusion, and form the rostrum; a longitudinal 

 line indicates the origin of this organ from two paired 

 halves ; and a pair of projections appear at the sides, 

 which later on become the maxillary palpi. The 

 fusion of the mandibular and maxillary knobs becomes 

 so complete that it is impossible to distinguish the 

 two ; it is only at a subsequent period that a division 

 once more appears in this homogeneous rostrum, by 

 means of which the maxillary lip and the mandibles 

 reappear as special, although greatly altered, organs. 



The leg-knobs gradually develop into sausage-shaped 

 appendages, lying against the ventral surface and 

 converging from behind forward. During later stages 

 of embryonic life the two anterior pairs of legs get 

 to bend backward ; at the same time they become 

 divided into joints, and the hairs upon them are formed. 

 The third pair of legs, however, always remain with 

 the tarsi pointing forward, and nearly touching the 

 rostrum : this third pair lies nearest to the ventral 

 surface, the two anterior pairs lie exterior to them. 

 At this period the anal slit becomes plainly visible. 

 Finally, when the embryo has acquired a chitinous 

 external layer, it has become a fully-formed larva, and 

 emerges. 



In Garpoglyphus, which is probably the only genus 

 of Tyroglyphidae provided with eyes, Kramer says * 

 that the eyes appear early in embryonic life. 



* " Ueber die postembryonale Entwicklung bei der Milbengattung 

 Glycyphagus " (1880), in ' Avcb. Naturg.,' Jahrg. xl, pp. 102110. 



