DEVELOPMENT AND IMMATURE STAGES. 129 



of the bird parasites above mentioned, not functional 

 as far as is known at present. Kramer stated that in 

 what he called Qlycyphagus the external sexual organs 

 appeared after the first ecdysis, and were therefore 

 present during the whole of the nymphal period 

 (although not functional). This would not be quite 

 correct if it really referred to Glycyphagus, but 

 Kramer's observations, which were carefully carried 

 out, were actually made upon Oarpoglyphus anonymus. 

 It may be broadly stated that great changes such 

 as exist in the life-histories of the Oribatidge, wherein 

 the whole appearance of the creature entirely alters, 

 so that there is but little resemblance between nymph 

 and imago, are not found in the Tyroglyphidee ; smaller 

 alterations of detail commonly exist, but as a rule the 

 one stage would be easily recognised by anyone ac- 

 quainted with the other. To this rule, however, there 

 is one notable exception, namely, the hypopial nymph, 

 when there is one ; during this portion of its life-history 

 the creature is entirely different from what it is at any 

 other time. 



THE OVUM. 



The eggs of the Tyroglyphidae are usually large in 

 proportion to the adult Acarus which deposited them, 

 but this is common in the Acarina ; they do not vary 

 greatly ; they are usually elliptical or oval and smooth, 

 without projections or any conspicuous decoration. 

 They are mostly white or light yellowish or greyish in 

 colour, and have a more or less soft outer covering, 

 not a rigid shell. This is probably the reason why the 

 deutovum stage, which is found in so many Acari which 

 lay eggs with a rigid, chitinised, external shell, does not 

 exist in the Tyroglyphidae ; the cuticle of the eggs of 

 these creatures appears to be capable of stretching 

 sufficiently for the needs of the egg. 



Embryology. There have been several valuable 

 contributions of late years to our knowledge of the 



9 



