
a ee 
240 THE NORTHERN MICROSCOPIST. 

OUR VERIFICATION DEPARTMENT. 
OR several months up to this date, pressure of business has 
compelled us to return objectives, sent into this department, 
unmeasured. We are now able to resume the work, but would call 
the attention of our readers to some slight changes in the condi- 
tions under which we undertake the verification. 
Hitherto we have charged a fee or eighteen-pence for each ob- 
jective ; we now propose to charge one shilling when the objective 
is without collar adjustment, and one shilling also for each series 
of measurements when the objective has a collar adjustment. In 
this latter case correspondents can have the measurements made 
at any one specified position of the collar, but if no mention is 
made of this, measurements will be made at the two extremes. 
The column denoting magnifying power has been omitted, it can, 
however be easily calculated from column d. 

THE CRAY FISH. 
S it is probably the privilege of comparatively few persons to 
see a cray fish cast its shell, a brief description of a case 
which recently came under observation may be of interest. _ First 
of all the carapace, or bony covering of the head and thorax, 
seemed to break away from its connection with the envelope of the 
abdomen. ‘The animal then stretched itself stiffly upon its left side 
on the shingle at the bottom of the aquarium, and proceeded to 
curl itself round, by which action the carapace above mentioned 
was brought well over the head, and the eyes were completely 
hidden from sight. At this stage it became evident that the 
abdomen also was beginning to recede from its case, and thus the 
process of “moving” went on simultaneously in both parts of the 
body, the swimmerets, ambulatory limbs, chelz, antennz, etc., all 
coming out perfect, the last-named, especially, being drawn out with 
the greatest ease as we might imagine a very flexible sword to be 
drawn from its sheath in an inconvenient position. When nothing 
but the extremities were left in the shell the animal gave a con- 
vulsive wriggle—the first symptom of impatience that it had 
betrayed—which set it completely free from its late tenement. 
After a few more wriggles, apparently to convince itself of the 
reality of what had just taken place, it relapsed into its normal 
condition of meditative apathy. The new shell was considerably 
darker than the old one, but soon toned down to the same hue. 
The original covering was taken out of the water and preserved in 
spirit; within two hours of its immersion its colour had changed 
from dark brown to a beautiful orange red. A. R. D. 



