CHANGE FROM NYMPH TO ADULT. 605 



from the rostrum and progaster of the nymphal skin 

 were measured from day to day with an eye-piece 

 micrometer. The investigation was not easy ; because 

 in order to see with sufficient clearness it was neces- 

 sary to use transmitted hght and this prevented 

 my covering the whole bottom of the inside of the 

 cell with blotting-paper, which is my usual mode of 

 preserving the desired hydrometric condition; from 

 this cause a larger proportion of the specimens died 

 than has been usual in other cases of rearing the 

 nymphs as mentioned in this book. 



The results were not altogether satisfactory, being 

 somewhat contradictory in the two species, but yet 

 perhaps they will be considered of sufficient interest 

 to be worth recording. The general conclusions come 

 to, so far as I was able to arrive at any, were : 



Firstly, that it is not the fact that in every species 

 and in every instance there is a complete breaking-up 

 and dissolution of all the organs of the nymph prior 

 to the formation of the adult ; but that, on the con- 

 trary, in some cases at all events, some of the internal 

 organs of the nymph are transferred to the adult and 

 are not dissolved but are identical in both stages. 



Secondly, that where dissolution and reformation 

 have occurred in the specimens which I have observed 

 the two processes have gone on simultaneously, and 

 there has not been any time when the cuticle contained 

 plastic or liquid matter only without any organs. 



Thirdly, that in the earlier stages of the change the 

 contents of the nymphal skin have (in the observed 

 instances) shrunk backward toward the posterior por- 

 tion of the creature, leaving the cuticle of the rostrum, 

 &c., empty, and that the contents of the legs have been 

 withdrawn or shrunk inward into the body-substance, 

 leaving the cuticle of the legs empty. 



Fourthly, that in the later stages of formation the 

 organs of the adult have again advanced forward nearer 

 to the rostrum of the nymphal cuticle, but not as far 

 forward as the old organs originally were. 



