390 E. R. Downing, 
Staining. 
A variety of stains were used after fixation in each of the above 
mentioned methods so as to determine what combination would give 
the best results. Iron haematoxylin, Bordeaux red. orange G, safra- 
nin, gentian violent, thionin, Kernschwarz, erythrosin, cyanin, Lyons 
blue, Bronpt, GRENACHER’S borax carmine, lithium carmine, and para- 
carmine were among the successful stains tried. The first five gave 
the best results. The iron haematoxylin was used with the Bordeaux 
red or the orange G and the safranin with the gentian violet or 
often alone. 
Mounting. 
Clearing was done in oil of bergamot or cedar oil and the 
sections mounted either in thick cedar oil or balsam. The best 
results were obtained, both regards preservation and stain, from the 
osmic MERKEL, preferably, or the Prereny1 followed by iron haema- 
toxylin and Bordeaux red or for count of chromomeres by safranin. 
Gentian violet was the best stain to differentiate the gland cells of 
the endoderm and was used after iron haematoxylin. In using 
safranin and gentian violet, BrzzozEro’s adaptation of Gram’s iodine 
method was not found to improve the results though tried repeat- 
edly, as were several similar methods. 
Ectoderm and endoderm. 
The ectoderm and endoderm cells are, roughly speaking, prisms, 
polygonal in cross sections or as seen from the surface of the animal. 
These prismatic cells have a greater or less altitude according as 
the animal is more or less extended. Their free bases are somewhat 
rounded surfaces. Intercellular spaces are of frequent occurrence, 
especially in the ectoderm. The protoplasm of the ectoderm cell (of 
endoderm also) appears to be composed of a mesh work. Indistinet 
anastomosing strands of a fairly dense material inclose a more fluid 
substance. Frequently the cell protoplasm is very vacuolate so that 
there will be a peripheral layer of protoplasm and strands of proto- 
plasm suspending the nucleus, but the bulk of the space between 
cell wall and nuclear wall is occupied by several large vacuoles. 
The nucleus also is reticular, is granular and contains one or more, 
usually one, nucleoli. 
Interstitial cells. 
Lying between the inner end of the ectoderm cells, though 
sometimes extending up between them nearly to the surface, are the 
- 
