134 lUUTlSH 



The nymphal stage is the great period of growth in 

 the Tyroglyphida3 and in most other Acarina : in the 

 Tyroglyphidse it is strictly the period between the 

 acquisition of the fourth pair of legs and that of the 

 genital organs becoming functional ; it also corresponds 

 to the interval between the first and the last ecdysis. 



With regard to the number of nymphal ecdyses 

 there are, as far as I know, only two existing authori- 

 ties, namely, Kramer and Nalepa; for although 

 Canestrini joined with Kramer, in " Das Thierreich,"* 

 in stating that all the Sarcoptidae, of which the Tyro- 

 glyphidse are there treated as a sub -family although 

 Canestrini considered them a family,t are binymphal ; 

 yet the portion of the joint work which dealt with the 

 Tyroglyphidae was by Kramer alone. Both he and 

 Nalepa had previously stated, as the result of their 

 observations, that the Tyroglyphidae underwent two 

 nymphal ecdyses only. Both these authors used the 

 same species for their investigations, viz. Carpoglyplms 

 anonymusyl and I am not aware that either stated 

 exactly how the facts had been ascertained. Unfortu- 

 nately Dr. Kramer's observations in this matter were 

 manifestly unreliable, because he stated that there was 

 not any inert period before the change of skin ; this is 

 an entire mistake, and no observer who had conducted 

 his research with sufficient care to make his results 

 reliable could possibly have missed it. The inert 

 period occurs before every ecdysis, and usually lasts 

 some days ; during it the creature is perfectly motion- 

 less and remains with outstretched or curled-up legs as 

 if dead, but it does not shrivel up. I have seen it 

 many hundreds of times, and have watched the 

 creatures gradually becoming inert, and, as will be 

 seen below, counted the time that the period lasted 

 over and over again. Nalepa pointed out Kramer's 



* Lief. 7, p. 4. 



f Ibid., note, p. 8. 



J Kramer, " Ueber die postembryonale Entwicklung bei der Milben- 

 gattung Glyciphagus" in 'Arch. Naturg.,' Jahrg. xl, Bd. i, p. 102. 

 Nalepa, Abth. 2. 



