84 MCMURRICH. [Vou. XIV. 
which have not been compelled to fast for some time, were 
washed away, the gut was then opened lengthwise with fine 
scissors and spread out upon a glass slide, where it was sub- 
jected to the action of the fixing reagent. Ide’s method of 
fixing the animal on a block of paraffin and carefully dissecting 
out the entire digestive tract was also used, but the more rapid 
method was found to be quite as satisfactory for the purposes 
I had in view. 
The fluid in which the animal was immersed was either 
water, normal salt solution, or corrosive sublimate; the last 
being used only for the purpose of control. For fixing I 
employed corrosive sublimate, Hermann’s and Flemming’s 
fluids, and found all three equally good, though I made use 
mainly of corrosive sublimate. In staining, various reagents 
were employed; for flat preparations alum cochineal and alum 
carmine were very satisfactory, but Delafield’s hzematoxylin, 
well washed out with acid alcohol, proved most so. Sections 
were also stained with these reagents and with Haidenhain’s 
iron-lack haematoxylin, which gave excellent and most instruc- 
tive preparations. The Biondi-Ehrlich stain was also used, and 
gave valuable information as to the nuclear constituents, and 
Korschelt’s combination of borax carmine and bleu de Lyon 
also proved useful. 
iT. 
Before entering upon the description of the epithelium it will 
be necessary to explain two terms that will be used. What will 
be meant by the mzdgut is that portion of the digestive tract 
which extends from the point where the liver czeca open to the 
beginning of the rectum, The term midgut is usually applied 
to a portion of a digestive tract which has an endodermal origin; 
the Isopod “ midgut,”’ however, is the anterior part of the proc- 
todzal invagination, and is not, therefore, entitled to be termed 
a midgut. It seems, however, more convenient to use the term 
midgut in the following pages than to invent a new term or 
employ a cumbersome periphrasis, but to avoid possible misun- 
derstanding I shall use the term only within quotation marks. 
The other term whose use I wish to explain is the word ce//. 
