604 BKITISII 0RI13ATID.E. 



THE FINAL CHANGE FROM NYMPH TO IMAGO. 



In vol. i of this work, at pp. 85, 8G, it has been 

 pointed out that considerable differences of opinion 

 had existed between acarologists as to whether the 

 whole substance of the nymph of one of the Acarina 

 (except the skin) dissolved and became plastic prior 

 to the formation of the adult, which was subsequently 

 developed from the general body-substance; or whether 

 the dissolution was at most only partial, the greater 

 part of the organs remaining intact, and the process 

 more resembling a mere change of skin. I mentioned 

 that in the case of the Orihatidce I was inclined to the 

 former view, which w^as that held by Megnin and others. 

 Since the publication of vol. i a considerable doubt 

 has arisen in my mind as to whether the dissolving 

 process was always complete ; and I have therefore 

 endeavoured to ascertain whether any light could be 

 thrown upon the question by obtaining very trans- 

 parent nymphs, which had highly coloured and con- 

 spicuous internal organs, and watching them frequently 

 during the change. The species which I selected for 

 observation were Notaspis bipilis and Notaspis liicorum ; 

 these were selected because their nymphs have smooth, 

 colourless, and highly transparent cuticles, but have 

 the alimentary canal and its glandular and other 

 appendages strongly coloured and conspicuous ; more- 

 over they are common species. 



Each creature to be observed was placed in a sepa- 

 rate glass cell without any other Acarina, and each 

 cell was numbered so as to avoid any possibility of 

 mistake ; only a very small number of specimens were 

 observed during the same period, fresh specimens not 

 being started until the old ones had emerged or died ; 

 this was in order that the exact appearance of each 

 specimen should be remembered from one inspection 

 to the next. The distances of the more conspicuous 

 internal organs, such as the preventricular glands, 



