THOMPSON: METAMORPHOSES OF HERMIT CRAB. 
159 
probably a still longer time must elapse before sexual maturity is 
attained. In the young females the rudiment on the second seg¬ 
ment begins to develop into a perfect pleopod at about thirty days 
from the glaucothoe. The remaining pleopods, and in many 
instances, this one also, do not begin to alter to the female type 
until ten days later, and the development of this type requires 
several moults for its full completion. 
The sixth stage was figured by Faxon (’82), and described by 
Agassiz (’75) as “ stage when the} 7 need a shell.’' 1 The later ado¬ 
lescent stages have not been recorded by anyone. 
Special Account of the Metamorphosis. 
The account of the development that has already been given 
has briefly described the plan of the anatomy in the larval stages 
and shown how this gives place to the adult type of structure in 
the glaucothoe phase. In the present chapter it is proposed to 
discuss in more detail the larval anatomy and the modifications by 
which the adult type is produced. 
Technique .— In this work, microscopical examination of living 
larvae or of specimens cleared in cedar oil gave only dubious results 
and therefore it was necessary throughout to employ serial sections. 
No killing fluid was uniformly satisfactory because of the difficulties 
of penetration and because the same tissues in different stages do 
not react in the same way to a reagent. The best and most reliable 
solutions used were a saturated aqueous solution of picric acid, five 
percent picro-acetic, and the stronger solution of Flemming. The 
brown stain produced in the contents of the liver cells was a serious 
objection to the use of the otherwise excellent reagents of the vom 
Rath series, and the lime salts in the integument in all stages barred 
picrosuiphuric. Perenyi’s fluid and corrosive sublimate in its various 
forms, the latter admitted by incision, though they frequently gave 
excellent fixations, were uncertain in action. 
To prevent injury to the delicate tissues after fixation, all the mate¬ 
rial was imbedded in paraffin from xylol as soon as possible. The 
integument in this connection offered no obstacle to penetration or 
dehydration. In sectioning, however, it was troublesome, forcing 
me to cut with a thickness of ten micra. Selective staining was 
